Question

If sin=3/5 then what cos equal to

Answer 1

$\sin {}^{2} ( \alpha ) + \cos {}^{2} ( \alpha ) = 1$
$\frac{9}{25} + \cos {}^{2} ( \alpha ) = 1$
$\cos {}^{2} ( \alpha ) = \frac{16}{25}$
$\cos( \alpha ) = \frac{4}{5}$

Answer 2

$\sin x=\dfrac{3}{5}\\ \sin^2x+\cos^2 x=1\\ \cos^2 x=1-\sin^2 x\\ \cos x=\sqrt{1-\sin^2 x} \vee \cos x=-\sqrt{1-\sin^2 x}\\\\ \cos x=\sqrt{1-\left(\dfrac{3}{5}\right)^2} \vee \cos x=-\sqrt{1-\left(\dfrac{3}{5}\right)^2}\\\\ \cos x=\sqrt{1-\dfrac{9}{25}} \vee \cos x=-\sqrt{1-\dfrac{9}{25}}\\\\ \cos x=\sqrt{\dfrac{16}{25}} \vee \cos x=-\sqrt{\dfrac{16}{25}}\\\\ \boxed{\cos x=\dfrac{4}{5} \vee \cos x=-\dfrac{4}{5}}$