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Answer 1 · 2018-02-01T09:04:33

#cos(x)=+-sqrt(1-sin^2(x))#

Use the pythagorean trigonometric identity:

#sin^2(x)+cos^2(x)=1#

Solve for cosine

#cos(x)=+-sqrt(1-sin^2(x))#

And then substitute your value for sine

Be aware of the sign

For each angle, there is only one value for cosine (or sine)

In quadrant 1 and 4 cosine is positive

In quadrant 2 and 3 cosine is negative