if sin x = .42, what is cos x?
\(We\ know:\\\\\sin^2x+\cos^2x=1\to\cos^2x=1-\sin^2x\to\cos x=\sqrt{1-\sin^2x}\\\\\sin x=0.42\\subtitute\\\\\cos x=\sqrt{1-0.42^2}=\sqrt{1-0.1764}=\sqrt{0.8236}\approx0.91\)
