Question

Angle 0 lies in the second quadrant and sin 0 = 3/5 cos= coy =

Answer 1

Consider the right triangle ABC with legs AB=4, AC=3 and hypotenuse BC=5. Angle B has
 $\sin B=\frac{opposite}{hypotenuse} = \frac{3}{5}$ and
 $\cos B = \frac{adjacent}{hypotenuse} = \frac{4}{5}$.

Since O lies in second quadrant $\cos O\ \textless \ 0$ and 
$\cos O= -\cos B =- \frac{4}{5}$.
Answer: $\cos O=- \frac{4}{5}$.