Question

Найдите cosα

, если sinα = − √ 51/10
и α ∈ ( π; 3п/2)


.

Answer 1

$sin alpha =-frac{sqrt{51}}{10},quad cos alpha <0,t.k.; alpha in (pi ,frac{3pi }{2})$

$cos alpha =-sqrt{1-cos^2 alpha }=-sqrt{1-frac{51}{100}}=-sqrt{frac{49}{100}}=- frac{7}{10}$