Question

Please help me out please!! :)

Answer 1

Starting from the Pythagorean identity, we deduce

$\sin^2(x)+\cos^2(x) = 1 \iff \cos^2(x) = 1-\sin^2(x) \iff \cos(x) = \pm\sqrt{1-\sin^2(x)}$

If we plug in the value 7/10 for sin(x), we have

$\cos(x) = \pm\sqrt{1-\dfrac{49}{100}} = \pm\sqrt{\dfrac{51}{100}}=\pm\dfrac{\sqrt{51}}{10}$