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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 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?

EduRev Class 9 answered
Let's analyze the given information step by step to determine whether triangles ΔABC and ΔPBC are congruent.
  1. Given:
    • AB = BP
    • AC = PC
    • BC = BC (common side)
  2. Triangles Involved:
    • ΔABC with sides AB, BC, and AC.
    • ΔPBC with sides PB (which is equal to AB), BC, and PC (which is equal to AC).
  3. Corresponding Sides:
    • AB corresponds to BP
    • AC corresponds to PC
    • BC corresponds to BC
  4. Applying the SSS Congruence Theorem:
    The Side-Side-Side (SSS) Congruence Theorem states that if all three corresponding sides of two triangles are equal in length, then the triangles are congruent.
    • AB = BP (First pair of corresponding sides)
    • AC = PC (Second pair of corresponding sides)
    • BC = BC (Third pair of corresponding sides, common side)
    Since all three pairs of corresponding sides are equal, ΔABC ≅ ΔPBC by the SSS Congruence Theorem.

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.

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.

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.

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 △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

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 

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 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°

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.

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

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.

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.

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 ABC and triangle DEF, if AB/DE = AC/DF = BC/EF, then the triangles are:
  • a)
    Similar
  • b)
    Congruent
  • c)
    Isosceles
  • d)
    None of the above
Correct answer is option 'A'. Can you explain this answer?

Explanation: This is the SSS similarity criterion, which states that if the sides of two triangles are in proportion, the triangles are similar

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.

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.

In fig, AC = BC and ∠ACY = 140. Find X and Y:
  • a)
    95and 150
  • b)
    110 and 110
  • c)
    50 and 120
  • d)
    80∘ and 80
Correct answer is option 'B'. Can you explain this answer?

Imk Pathshala answered
∠ACB = 40ο
as ABC is a isoceles trinagle
so ∠BAC = ∠ABC = a
a + a + 40 = 180ο
2a = 140ο 
a = 70ο
x + a =180ο   and  y +a = 180ο
x = 110ο  and y = 110ο

In ΔABC if ∠A = ∠B, then
  • a)
    AC ≠ BC
  • b)
    AC = BC
  • c)
    AB = AC
  • d)
    AB = BC
Correct answer is option 'B'. Can you explain this answer?

Game Killer answered
Becuase Sides opposite to equal angles are also equal.angle A = angle BBC is opposite to angle A and AC is opposite to angle B.Therefore, AC=BC in triangle ABC.

If the bisector of the exterior vertical angle of a triangle is parallel to the base, then it is
  • a)
    Isosceles triangle
  • b)
    Scalene triangle
  • c)
    Right angled triangle
  • d)
    Equilateral triangle
Correct answer is option 'A'. Can you explain this answer?

∠CAE is the external vertical angle and AD is its bisector.
 
∴ ∠CAD = ∠DAE  .... (i)
 
As, AD || BC
 
∴ ∠CAD = ∠ACB  .... (ii)  (alternate angle)
 
and ∠DAE = ∠ABC  ....(iii)  (corresponding angle)
 
From (i), (ii) and (iii),
 
∠ABC = ∠ACB
 
∴ AC = AB  (opposite sides to equal angles)
 
Hence, ΔABC is isosceles.

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 △ABC, if ∠B = 30 and ∠C = 70, then which of the following is the longest side?
  • a)
    AB
  • b)
    BC
  • c)
    AC
  • d)
    AB or AC
Correct answer is option 'B'. Can you explain this answer?

You are referring to a triangle, then the statement is incomplete. Please provide more information about the triangle and your question.

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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