Question

If sinx = 0.3, and x is in Quadrant III, then what is the value of cosx?

Answer 1

√0.91

Explanation:

I got it correct on Odyssey

Answer 2

Probably the question should say
`\sin x=-0.3`, as
`\sin x` is negative for
`\pi<x<\frac{3\pi}2`.

In that case, recall that

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

Because
`x` lies in the third quadrant, we expect
`\cos x` to also be negative, so we take the negative root above. Then

`\cos x=-√(1-(-0.3)^2)\approx-0.954`