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All questions of Triangles for Class 9 Exam

In the adjoining figure, BC = AC. If ∠ACD = 115, the ∠A is
  • a)
    70
  • b)
    57.5
  • c)
    65
  • d)
    50
Correct answer is option 'B'. Can you explain this answer?

C K Academy answered
In △ABC,
∠ACD+∠ACB = 180 (Linear pair)
115+∠ACB =180
∠ACB = 180−115=65
x + x + 65 = 180
2x = 180- 65
2x = 115
x = 57.5

In the given figure, ABC is an equilateral triangle. The value of x+y is 
  • a)
    120
  • b)
    200
  • c)
    240
  • d)
    180
Correct answer is option 'C'. Can you explain this answer?

Hrid Deb answered
It is equilateral triangle
so all the sides will be equal
The measure of one side = 180÷3
= 60
the exterior angle will be equal so
=180-60
= 120 sum of the angles are= 120+120
= 240
So option C is correct.

In ΔABC and ΔPBC, AB = BP and AC = PC. Can you say whether the triangles are congruent to each other or not:
  • a)
    Yes, by ASA Congruence theorem they are congruent
  • b)
    Yes, by SAS Congruence theorem they are congruent
  • c)
    No, they are not congruent
  • d)
    Yes, by SSS Congruence theorem they are congruent
Correct answer is option 'D'. Can you explain this answer?

Sachi Shah answered
Given that AB = BP and AC = PC, we need to determine whether triangles ABC and PBC are congruent or not. Let's analyze the options one by one.

a) Yes, by ASA Congruence theorem they are congruent.
According to the ASA (Angle-Side-Angle) Congruence theorem, two triangles are congruent if they have two corresponding angles and the included side equal. However, in this case, we only know that the corresponding sides are equal, but we don't have any information about the angles. Therefore, we cannot conclude that the triangles are congruent using the ASA Congruence theorem.

b) Yes, by SAS Congruence theorem they are congruent.
According to the SAS (Side-Angle-Side) Congruence theorem, two triangles are congruent if they have two corresponding sides and the included angle equal. In this case, we have AB = BP and AC = PC, which are the corresponding sides, but we don't have any information about the included angle. Therefore, we cannot conclude that the triangles are congruent using the SAS Congruence theorem.

c) No, they are not congruent.
This option suggests that the triangles are not congruent without providing any reasoning. We cannot simply say that the triangles are not congruent without any valid justification.

d) Yes, by SSS Congruence theorem they are congruent.
According to the SSS (Side-Side-Side) Congruence theorem, two triangles are congruent if they have three corresponding sides equal. In this case, we have AB = BP and AC = PC, which are the corresponding sides. Additionally, we know that BC = BC since it is a common side. Therefore, all three corresponding sides of the triangles are equal, satisfying the condition for congruence by the SSS Congruence theorem. Hence, we can conclude that the triangles ABC and PBC are congruent.

In conclusion, the correct answer is option 'd'. The triangles ABC and PBC are congruent by the SSS Congruence theorem as all three corresponding sides are equal.

In triangle PQR length of the side QR is less than twice the length of the side PQ by 2 cm. Length of the side PR exceeds the length of the side PQ by 10 cm. The perimeter is 40 cm. The length of the smallest side of the triangle PQR is :
  • a)
    6 cm
  • b)
    8 cm
  • c)
    7 cm
  • d)
    10 cm
Correct answer is option 'B'. Can you explain this answer?

Given:
- QR < 2pq="" -="" />
- PR = PQ + 10
- PQ + QR + PR = 40

To find:
The length of the smallest side of the triangle PQR.

Solution:

1. Simplify the first equation:
QR < 2pq="" -="" 2="" />
QR + 2 < 2pq="" />
PQ > (QR + 2)/2

2. Substitute PR and PQ in terms of QR in the third equation:
PQ + QR + PR = 40
((QR + 2)/2) + QR + ((QR + 2)/2 + 10) = 40
3QR + 14 = 40
3QR = 26
QR = 8.67

3. Substitute QR into the first equation to find PQ:
PQ > (QR + 2)/2
PQ > (8.67 + 2)/2
PQ > 5.34

4. Substitute PQ and QR into the second equation to find PR:
PR = PQ + 10
PR = 5.34 + 10
PR = 15.34

5. Check that the sum of all sides is 40:
PQ + QR + PR = 5.34 + 8.67 + 15.34 = 29.35

6. Since PQ is the smallest side, the answer is 8 cm (rounded to the nearest whole number).

Therefore, the length of the smallest side of the triangle PQR is 8 cm.

In the adjoining figure, the rule by which △ABC ≅ △ADC
  • a)
    AAS
  • b)
    RHS
  • c)
    SSS
  • d)
    SAS
Correct answer is option 'C'. Can you explain this answer?

Let's Tute answered
In the given figure, we need to determine the rule by which ∆ABC is congruent to ∆ADC.
Observations:
  • Side AC: This side is common to both triangles.
  • Side AB = AD: Both sides are 4 cm.
  • Side BC = CD: Both sides are 2.7 cm.
Rule for Congruence:
Since all three corresponding sides of the triangles are equal (AB = AD, BC = CD, AC = AC), the triangles satisfy the Side-Side-Side (SSS) congruence rule.
Correct Answer:
c) SSS

In the adjoining fig, PQ = PR. If ∠QPR = 48, then value of x is:
  • a)
    114
  • b)
    96
  • c)
    132
  • d)
    104
Correct answer is option 'A'. Can you explain this answer?

EduRev Class 9 answered
- In triangle PQR, PQ = PR , making it an isosceles triangle.
- In an isosceles triangle, the angles opposite the equal sides are equal.
- Given angle QPR = 48 degrees ,
let angle PQR = angle PRQ = y
- The sum of angles in a triangle is  180.
- Therefore, y + y + 48 = 180
- Solving: 2y = 132 degrees
therefore y = 66 degrees
 angle y + angle x = 180 degrees
66 + angle x = 180 degree 
angle x = 180-66
angle x = 132 degree 

If the bisector of the angle A of a △ABC is perpendicular to the base BC of the triangle then the triangle ABC is :
  • a)
    Obtuse Angled
  • b)
    Isosceles
  • c)
    Scalene
  • d)
    Equilateral
Correct answer is option 'B'. Can you explain this answer?

Imk Pathshala answered
If the bisector of angle A of a triangle is perpendicular to the base BC of the triangle then the triangle ABC is:

B: Isosceles

Solution:

- The angle bisector of angle A divides the angle into two equal parts.
- For this bisector to be perpendicular to base BC, angles B and C must be equal.
- This means that triangle ABC has two equal sides opposite these equal angles.
- Therefore, triangle ABC is isosceles.

In the adjoining figure, BC = AD, CA⊥AB and BD⊥AB. The rule by which △ABC ≅ △BAD is
  • a)
    ASA
  • b)
    SAS
  • c)
    RHS
  • d)
    SSS
Correct answer is option 'C'. Can you explain this answer?

Sohan Mandal answered
In ∆ABC and ∆BAD,
AB = common side
BC = AD ( given , side opposite to right angle of a
triangle is it's hypotenuse )
angle CAB = angle ABD( right angle )
therefore, ∆ABC and ∆BAD are congruent by RHS rule of congruence

In △ABC, AB=5 cm and BC=6 cm. Then, the length of AC cannot be
  • a)
    3.8 cm
  • b)
    3.4 cm
  • c)
    4cm
  • d)
    3.6 cm
Correct answer is option 'B'. Can you explain this answer?

Ananya Das answered
in triangle ABC
AB = 2.5 cm
BC = 6 cm
AC =  ?
in any triangle sum of two sides >  third side
=> AB +  BC > AC
=> 2.5 + 6 > AC
=> AC < 8.5
AB + AC > BC
=> 2.5 + AC > 6
=> AC > 3.5
BC + AC > AB
=> 6 + AC > 2.5
=> AC > -3.5
Taking all together
 3.5 < AC  < 8.5
3.6 ,  3.8 & 4  lies betwenn them
but not 3.4
Hence Length of AC can not be 3.4 cm

If the altitudes from two vertices of a triangle to the opposite sides are equal, then the triangles is
  • a)
    Scalene
  • b)
    Isosceles
  • c)
    Equilateral
  • d)
    Right-angled
Correct answer is option 'B'. Can you explain this answer?

Swati Verma answered
Given:
BE = CD
Concept Used:
When 2 sides of a triangle are equal, then it is isosceles.
When 2 angles and 1 side of 2 triangles is equal, then both the triangles are similar.
Calculations:
In △ABE and △ACD,
BE = CD (Given)
∠BEA = ∠CDA (90° each)
∠BAE = ∠CAD (Common Angle)
∠ABE = ∠ACE (By Sum angle property)
⇒ △ABE is similar to △ACD
⇒ AB = AC
∴ If the altitudes from two vertices of a triangle to the opposite sides are equal, then the triangle is isosceles.

It is not possible to construct a triangle when its sides are:
  • a)
    6 cm, 7 cm, 7 cm
  • b)
    5.4 cm, 2.3 cm, 3 cm
  • c)
    8.3 cm, 3.4 cm, 6.1 cm
  • d)
    3 cm, 5 cm, 5 cm
Correct answer is option 'B'. Can you explain this answer?

Dipika Chopra answered
Explanation:

To construct a triangle, the sum of the lengths of any two sides must be greater than the length of the third side. This is known as the triangle inequality theorem. Let's check each option:

a) 6 cm, 7 cm, 7 cm
- 6 + 7 > 7, 7 + 7 > 6, 6 + 7 > 7
- The sum of any two sides is greater than the third side, so it is possible to construct a triangle with these side lengths.

b) 5.4 cm, 2.3 cm, 3 cm
- 5.4 + 2.3 < 3,="" 5.4="" +="" 3="" />< 2.3,="" 2.3="" +="" 3="" />< />
- The sum of the lengths of the two smaller sides is less than the length of the largest side, so it is not possible to construct a triangle with these side lengths.

c) 8.3 cm, 3.4 cm, 6.1 cm
- 8.3 + 3.4 > 6.1, 8.3 + 6.1 > 3.4, 3.4 + 6.1 > 8.3
- The sum of any two sides is greater than the third side, so it is possible to construct a triangle with these side lengths.

d) 3 cm, 5 cm, 5 cm
- 3 + 5 > 5, 3 + 5 > 5, 5 + 5 > 3
- The sum of any two sides is greater than the third side, so it is possible to construct a triangle with these side lengths.

Therefore, the correct answer is option B, as it is not possible to construct a triangle with side lengths 5.4 cm, 2.3 cm, and 3 cm.

In two right triangles, one side and an acute angle of one are equal to the corresponding side and angle of the other, then ΔABC ≅ ΔDEF by the criterion
  • a)
    ASA
  • b)
    AAS
  • c)
    SSS
  • d)
    SAS
Correct answer is option 'B'. Can you explain this answer?

Aayan Hooda answered
It is given that angle A and angle D are equal. It is given that angle B and Angle E are equal. it is given that line CB is equal to the line FE. Because of these things ∆ABC is congruent to ∆DEF.

Choose the correct statement
  • a)
    Two right triangles are congruent, if hypotenuse and a side of one are respectively equal to the hypotenuse and a side of the other triangle
  • b)
    If thee altitude from one vertex of a triangle bisects the opposite side, then the triangle may be isosceles
  • c)
    If any two sides of a right triangle are respectively are equal to two sides of the other right triangle, then the two triangles are congruent
  • d)
    Sides opposite equal angles may be unequal
Correct answer is option 'A'. Can you explain this answer?

Let's Tute answered
Answer: A
Explanation:
Option A is correct because the Hypotenuse-Side (HS) congruence criterion states that if the hypotenuse and one side of one right triangle are equal to the hypotenuse and one side of another right triangle, the two triangles are congruent.
Other options are incorrect:
  • B: This statement is partially correct but not universally true for all cases, as the altitude bisecting the opposite side guarantees an isosceles triangle only under specific conditions.
  • C: The congruence of two right triangles cannot be guaranteed if just any two sides are equal; the Hypotenuse-Leg or another criterion must be specified.
  • D: If the angles are equal, the opposite sides must also be equal, making this statement incorrect.

In triangle PQR, PQ = PR and R = 65°, then P = ?
  • a)
    75°
  • b)
    50°
  • c)
    40°
  • d)
    120°
Correct answer is option 'B'. Can you explain this answer?

Gaurav Kumar answered
By using the theorem,If two sides of a triangle are equal then the opposite angles to the sides are equal.
⇒ if PQ=PR then ∠Q=∠R
in triangle PQR,
⇒ ∠P+∠Q+∠R=180°
⇒ ∠P+∠Q+∠Q=180° (∵∠Q=∠R)
⇒ ∠P+65°+65°=180°
⇒ ∠P+130°=180°
⇒ ∠P=180°-130°
⇒ ∠P=50

In figure, ABCD is a quadrilateral in which AB = BC and AD = DC. Measure of ∠BCD is:
  • a)
    30
  • b)
    72
  • c)
    150
  • d)
    105
Correct answer is option 'D'. Can you explain this answer?

EduRev Class 9 answered
In ΔABC ,as it is isoceles so,
∠BCA=36°  [ (180°-108°)/2 ]
In ΔADC ,as it is isoceles so,
∠DCA=69°  [ (180°-42°)/2 ]
∠BCD=∠BCA+∠DCA
∠BCD=36°+69°
∠BCD=105°

Two equilateral triangles are congruent when:
  • a)
    Their areas are proportional
  • b)
    Their sides are equal
  • c)
    Their sides are proportional
  • d)
    Their angles are equal
Correct answer is option 'B'. Can you explain this answer?

EduRev Class 9 answered
Explanation: For two equilateral triangles to be congruent, their corresponding sides must be equal in length. In congruent triangles, all corresponding sides and angles are identical. While equilateral triangles always have equal angles (60°), congruence is specifically determined by the equality of sides.

In triangles ABC and DEF, AB = FD and ∠A=∠D. The two triangles will be congruent by SAS axiom if :
  • a)
    BC = EF
  • b)
    AC = EF
  • c)
    AC = DE
  • d)
    BC = DE
Correct answer is option 'C'. Can you explain this answer?

Hina Sharma answered
BC = EF. The angles ∠ABC and ∠DEF are also congruent. Therefore, the triangles ABC and DEF are congruent by the Side-Angle-Side (SAS) congruence criterion.

ABCD is a parallelogram, if the two diagonals are equal, then by what criterion are the triangles ABD and ABC congruent
  • a)
    AAS
  • b)
    SSS
  • c)
    SAS
  • d)
    RHS
Correct answer is option 'B'. Can you explain this answer?

Saksham Singh answered
In triangle ABD and ABC ( THE TRIANGLE ARE NOT IN ORDER)
i) AD=BC ( OPPOSITE SIDES OF PARALLELOGRAM ARE EQUAL)
ii) BD=AC ( GIVEN)
III) AB=AB ( COMMON)

therefore triangle ABD congruent triangle BAC ( BY SSS criteri

SO, CORRECT ANSWER IS OPTION B

In △ABC, ∠A = 35 and ∠B = 65, then the longest side of the triangle is:
  • a)
    AC
  • b)
    BC
  • c)
    AB
  • d)
    None of these
Correct answer is option 'C'. Can you explain this answer?

Anjali Singh answered
We have three sides AB, BC, and CA, and three angles A, B, and C. The sum of the angles in a triangle is always 180 degrees.

The perimeter of the triangle ABC is the sum of the lengths of its three sides, AB, BC, and CA. It is denoted as P.

The area of the triangle ABC can be calculated using different formulas depending on the given information. One common formula is the Heron's formula, which uses the lengths of the three sides. It is denoted as A.

Another formula to calculate the area of a triangle is by using the base and height. If we know the length of one side and the height from that side to the opposite vertex, we can use the formula A = (1/2) * base * height.

Is there anything specific you would like to know about triangle ABC?

In ΔABC if AB = BC then:
  • a)
    ∠A < ∠C
  • b)
    ∠C > ∠A
  • c)
    ∠A = ∠C
  • d)
    ∠B > ∠C
Correct answer is option 'C'. Can you explain this answer?

Rochana Singh answered
**Explanation:**

The given statement states that AB is equal to BC. Let's understand this statement and its implications in detail.

**Understanding the Statement:**
- AB = BC means the length of line segment AB is equal to the length of line segment BC.
- In simpler terms, the distance between point A and point B is the same as the distance between point B and point C.

**Implications:**
- If AB = BC, it implies that the triangle ABC is an isosceles triangle.
- An isosceles triangle is a triangle that has two sides of equal length.
- In this case, since AB = BC, the triangle ABC has two sides AB and BC that are equal.
- The third side AC can be of any length.

**Explanation of Options:**
a) A ≠ C: This option states that point A is not equal to point C. However, the given statement AB = BC does not provide any information about the equality of points A and C. So, this option is incorrect.
b) C ≠ A: This option states that point C is not equal to point A. Similar to the explanation for option a), the given statement AB = BC does not provide any information about the equality of points A and C. So, this option is incorrect.
c) A = C: This option states that point A is equal to point C. The given statement AB = BC does not directly mention anything about the equality of points A and C. However, since AB = BC, it implies that the two sides of the triangle ABC (AB and BC) are equal. And in an isosceles triangle, the angles opposite to the equal sides are also equal. So, angle A = angle C. Therefore, this option is correct.
d) B ≠ C: This option states that point B is not equal to point C. Similar to the explanation for option a), the given statement AB = BC does not provide any information about the equality of points B and C. So, this option is incorrect.

Therefore, the correct answer is option 'C' - A = C.

D is a Point on the Side BC of a △ABC such that AD bisects ∠BAC then:
  • a)
    BD = CD
  • b)
    CD > CA
  • c)
    BD > BA
  • d)
    BA > BD
Correct answer is option 'D'. Can you explain this answer?

Sarita Reddy answered
Correct, option 'D' is the correct answer.
When AD bisects ∠BAC, it means that angle BAC is split into two equal angles, BDA and BAC. Since BDA and BAC are equal, it means that angle BDA is half of angle BAC, and angle BAC is twice angle BDA.
Therefore, angle BAD is less than angle BAC.
As the angle BAC is greater than angle BAD, then it follows that side BA is greater than side BD.
Therefore, BA > BD.
In a triangle, the sum of the two smaller sides will always be greater than the largest side, which is called the triangle inequality theorem.

Pick out the incorrect statement
  • a)
    Sides opposite to equal angles are equal in a triangle
  • b)
    If the altitude from one vertex of a triangle bisects the opposite side, then the triangle is isosceles
  • c)
    If the bisector of the vertical angle of the triangle bisects the base of the triangle, then the triangle is isosceles
  • d)
    All the altitudes of an isosceles triangle are equal
Correct answer is option 'D'. Can you explain this answer?

Kavya Chavan answered
The altitudes of a triangle are the line segments drawn from each side of the triangle to the angle opposite that side, such that the line segment is perpendicular to the side it is drawn from. In an isosceles triangle, only the altitudes of the legs of equal length in the triangle are congruent. 

The altitude of an equilateral triangle of side a to any of its other sides from the opposite vertex is
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'A'. Can you explain this answer?

Charming Rocky answered
Option (a) is correct.. it can also be obtained by using Pythagoras theorem .. where base=a/2 and hypotenuse=a. .then altitude=. ...

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