Question

Evaluate : (i) Sin 18°/
Cos 72°​

Answer 1

Answer:

$\frac{ \sin(18) }{ \cos(72) } = \frac{ \sin(90 - 72) }{ \cos(72) } \\ = \frac{ \cos(72) }{ \cos(72) } \\ = 1$

We know that

$\sin(90 - theta) = \cos(theta)$

Answer 2

Answer:

Sin 18°/cos 72°

We can write sin as Cos 72°

( sin(90-A)=cos A)

(sin (90°-18°) = cos 72°)

( sin 72° = cos 72°)

So, cos 72°/cos 72° = 1