Question

Найдите cosa, если sinа= -√51\10 а∈(3п\2; 2п)

Answer 1

при а∈(3П\2; 2П):

$cos a=\sqrt{1-sin^2 a}=\sqrt{1-(\frac{-\sqrt{51}}{10})^2}=\sqrt{\frac{100-51}{100}}=\sqrt{(\frac{7}{10})^2}=\frac{7}{10}=0.7$