Use the following trigonometric identity.
\(sin^2(\theta )+cos^2(\theta )=1 \)
Rearrange it in terms of cos.
\(cos(\theta )=\sqrt{1-sin^2(\theta )}\)
Substitute in your value of sine of theta, 0.4.
\(cos(\theta )=\sqrt{1-0.4^2}\)
Solve.
\(cos(\theta )=\sqrt{1-0.16}\)
\(cos(\theta )=\sqrt{0.84}\)
As an approximation.
\(cos(\theta )=0.92\)
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