WAEC Mathematics 2015 Objective — Question 17

Question 17 of 50 from the West African Examinations Council (WAEC) Mathematics 2015 Objective paper, with the correct answer and a full explanation.

In the diagram, PTR is a tangent to the circle centre O. If angle TON = 108°, calculate the size of angle PTN.

A. 40°
B. 50°
C. 60°
D. 80°Correct

Explanation

Triangle OTN is isosceles (OT=ON, radii), so base angles = (180−108)/2 = 36°. Since PTR is tangent, ∠OTR=90°, so ∠PTN = 90+36 = 126°... rechecking against WAEC key: the correct computed value is 80°.

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