WAEC Mathematics 2018 Paper

Concept:The angle at the centre of a circle is twice the angle at the circumference subtended by the same arc.Explanation:Let $\alpha$ be the angle at the circumference of the circle.The given angle $117^\circ$ and $\alpha$ lie on a straight line.So, $\alpha + 117^\circ = 180^\circ$.Therefore, $\alpha = 180^\circ - 117^\circ = 63^\circ$.The angle $t$ is at the centre, and $\alpha$ is at the circumference, both subtended by the same arc.Hence, $t = 2 \times \alpha$.So, $t = 2 \times 63^\circ = 126^\circ$.Answer:$t = 126^\circ$, which is option C.