Question

Se cos x/2 = 3/4 , então cosx vale quanto?

Answer 1

Vamos la....

cos(x/2)=3/4

cosx = ?

Pelo arco duplo:

cosx = cos(2x/2) = [cosx/2]² - [senx/2]²

[senx/2]² = 1 - [cosx/2]²

cosx = cos(2x/2) = [cosx/2]² - 1 + [cosx/2]²

3/4 = cosx/2

cosx = cos(2x/2) = [3/4]² - 1 + [3/4]²

cos(2x/2) = 9/16 - 1 + 9/16

cos(2x/2) = 9/16 - 16/16 + 9/16 = 2/16 = 1/8