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AB is a chord of length 24 cm of a circle of radius 13 cm. The tangents at A and B intersect at a point C. Find the length AC.
  • a)
    31.2 cm
  • b)
    12 cm
  • c)
    28.8 cm
  • d)
    25 cm
Correct answer is option 'A'. Can you explain this answer?
Most Upvoted Answer
AB is a chord of length 24 cm of a circle of radius 13 cm. The tangent...
Given, Chord AB = 24 cm, Radius OB = OA = 13 cm.
Draw OP ⊥ AB
In D OPB, OP ⊥ AB ⇒ AP = PB
[Perpendicular from centre on chord bisect the chord] =(1/2)AB= 12
Also, OB2 = OP2 + PB2
⇒ (13)2 = OP2 + PB2 ⇒ 169 = OP2 + (12)2
⇒ OP2 = 169 - 144 = 25 ⇒ OP = 5 cm
In Δ BPC, BC2 = x2 + BP2 [By pythagoras theorem]
BC2 = x2 + 144 ...(i)
In ΔOBC, OC2 = OB2 + BC2
⇒ (x + 5)2 = (13)2 + BC2 ⇒ x = 288/10=28.8cm

Put the value of x in (i), we get
BC2 = x2 + 144 = ((144)2/25) + 144⇒ BC = 31.2
⇒ AC = BC = 31.2 cm
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Community Answer
AB is a chord of length 24 cm of a circle of radius 13 cm. The tangent...
To find the length AC, we need to apply the properties of tangents and chords in a circle.

Given:
Chord AB = 24 cm
Radius of the circle = 13 cm

Properties of Tangents and Chords:
1. The tangent to a circle is perpendicular to the radius drawn to the point of tangency.
2. Two tangents drawn from an external point to a circle are equal in length.

Let's solve the problem step by step:

Step 1: Draw the diagram
Draw a circle with center O and radius 13 cm. Mark a point C outside the circle. Draw tangents from C to the circle, which intersect the circle at points A and B.

Step 2: Identify the given information
We are given the length of chord AB, which is 24 cm, and the radius of the circle, which is 13 cm.

Step 3: Apply the properties of tangents and chords
Since the tangents from an external point to a circle are equal in length, we can conclude that CA = CB.

Step 4: Calculate the length of AC
Since CA = CB, we can consider CA as x and CB as x. Therefore, we have:
CA + AB + CB = 2x + 24 = perimeter of triangle ABC

Step 5: Calculate the perimeter of triangle ABC
The perimeter of triangle ABC can be calculated using the lengths of its sides.

We know that AB = 24 cm and the radius of the circle = 13 cm. The radius is perpendicular to the tangent at the point of tangency. Therefore, triangle ABC is a right-angled triangle.

Using Pythagoras' theorem, we can find the length of the hypotenuse (AB):

AB² = AC² + BC²
24² = x² + 13²
576 = x² + 169
x² = 576 - 169
x² = 407
x = √407

Step 6: Calculate the perimeter of triangle ABC
Using the lengths of the sides, we can calculate the perimeter of triangle ABC:

Perimeter of triangle ABC = 2x + 24
= 2(√407) + 24

Step 7: Simplify and find the value of the perimeter
Using a calculator, we can find the value of the perimeter of triangle ABC:

Perimeter of triangle ABC ≈ 31.2 cm

Therefore, the length of AC is approximately 31.2 cm.

Hence, the correct answer is option A) 31.2 cm.
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