Question

se sen a=5/13, com a ângulo agudo, encontre o valor de cos a?

Answer 1

$sen^2x + cos^2x = 1 \\ \\ ( \frac{5}{13} )^2 + cos^2a = 1 \\ \\ cos^2a = \frac{169}{169} - \frac{25}{169} \\ \\ cos^2a = \frac{144}{169} \\ \\ \boxed{\boxed{cosa = \frac{12}{13} }}$