Question

Вычислите sina, если cosa = 4/5, аЕ (0; П/2)

Answer 1

$cosalpha=frac{4}{5}; alphain(0; frac{pi}{2})\\sin^2alpha+cos^2alpha=1\\sin^2alpha+left(frac{4}{5}right)^2=1\\sin^2alpha+frac{16}{25}=1\\sin^2alpha=1-frac{16}{25}\\sin^2alpha=frac{9}{25}\\sinalpha=sqrtfrac{9}{25}\\sinalpha=frac{3}{5}$

Answer 2

:)

Answer 3

a∈I
$sina= sqrt{1-cos^{2} a} = sqrt{1- frac{16}{25} } = sqrt{ frac{9}{25} } = frac{3}{5}$