passpadi

2023

Mathematics

JAMB

The diagram above is a circle with centre C. P, Q and S are points on the circumference. PS and SR are tangents to the circle. ∠PSR = 36o . Find ∠PQR

A.

72o

B.

36o

C.

144o

D.

54o

Correct Answer: 72o

Explanation

From ∆PSR |PS| = |SR| (If two tangents are drawn from an external point of the circle, then they are of equal lengths) ∴ ∆PSR is isosceles ∠PSR + ∠SRP + ∠SPR = 180 o (sum of angles in a triangle) Since |PS| = |SR|; ∠SRP = ∠SPR ⇒ ∠PSR + ∠SRP + ∠SRP = 180o ∠PSR + 2∠SRP = 180o 36o + 2∠SRP = 180o 2∠SRP = 180o - 36o 2∠SRP = 144o ∠SRP = 144o/2=72o ∠SRP = ∠PQR (angle formed by a tangent and chord is equal to the angle in the alternate segment) ∴ ∠PQR = 72o

From ∆PSR |PS| = |SR| (If two tangents are drawn from an external point of the circle, then they are of equal lengths) ∴ ∆PSR is isosceles ∠PSR + ∠SRP + ∠SPR = 180 o (sum of angles in a triangle) Since |PS| = |SR|; ∠SRP = ∠SPR ⇒ ∠PSR + ∠SRP + ∠SRP = 180o ∠PSR + 2∠SRP = 180o 36o + 2∠SRP = 180o 2∠SRP = 180o - 36o 2∠SRP = 144o ∠SRP = 144o/2=72o ∠SRP = ∠PQR (angle formed by a tangent and chord is equal to the angle in the alternate segment) ∴ ∠PQR = 72o
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