Question

найдите Cosa, если Sina=-12/13, п<a<3п/2

Answer 1

$Cos A = - \sqrt{1 - sinA^{2} } = - 5/13$
Ответ: - 5/13

Answer 2

соs²a=1-sin²x=1-(-12/13)²=1-144/169=
25/169
π<a<3π/2
cosa=-√(25/169)=-5/13