Question

Знайти Cos2a якщо Sina=$\frac{1}{4}$

Answer 1

cos2a = (1 - 2sin^2a)
sin^2a = 1/4^2 = 1/16
1 - 2*1/16 = 1 - 1/8 = 7/8 =>
cos2a = 0,875

Answer 2

Ответ:

Объяснение:

$sina=\frac{1}{4};\\sin^2a+cos^2a=1;cos^2a=1-sin^2a=1-(\frac{1}{4})^2=1-\frac{1}{16}=\frac{15}{16};\\cos2a=cos^2a-sin^2a=\frac{15}{16}-\frac{1}{16}=\frac{14}{16}=\frac{7}{8}$