Question

Sin theta =3/5 and theta lie in quadrant ii . What is cos theta

Answer 1

`\cos^2\theta+\sin^2\theta=1\implies\cos\theta=\pm√(1-\sin^2\theta)`

Because
`\theta` lies in quadrant II, we can expect
`\cos\theta` to be negative, so we take the negative root.

This leaves us with


`\cos\theta=-√(1-\left(\frac35\right)^2)=-\frac45`