Test Index

WAEC Mathematics 2017 Paper

Question : 37

Total: 49

Solution:

Concept:

Angle at the centre is twice the angle at the circumference on the same chord.

Equal radii form isosceles triangles.

Explanation:

Take the marked diagram values as

\angle RST = 46^\circ

and

\angle STR = 29^\circ

The central angle subtending chord

RT

\angle ROT

So,

\angle ROT = 2 \times \angle RST = 2 \times 46^\circ = 92^\circ

\triangle ROT

OR = OT

since both are radii.

Hence,

\angle RTO = \frac{180^\circ - 92^\circ}{2} = 44^\circ

From the diagram, the ray

TS

lies between

TR

and

TO

Therefore,

\angle RTO = \angle RTS + \angle STO

44^\circ = 29^\circ + \angle STO

Thus,

\angle STO = 44^\circ - 29^\circ = 15^\circ

Answer:

\angle STO = 15^\circ

, so option B is correct.

Go to Question:

Prev Question

Next Question