Q) The length of a tangent from point A at a distance 5 cm from the centre of the circle is 4 cm. Find the radius of the circle.

9th Class Maths – NCERT Important Questions

Ans:

Step 1:

Let’s make a diagram for better understanding of the question:

Given that the distance OA = 5 cm, AB = 4 cm. We need to calculate value of Radius OB.

Step 2: 

Since the radius is perpendicular to tangent

∴ ∠ OBA = 90⁰

Step 3: 

Next in Δ OBA, OB ² + AB ² = OA ²

∴ OB ² + (4) ² = (5) ²

∴ OB ² + 16 = 25

∴ OB ² = 25 – 16 = 9

∴ OB = 3 cm

Therefore, the radius of the circle is 3 cm

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