Question

Dado cos x = 5/13, com 3pi/2 < x < 2pi, calcule o valor de cos(x + pi/4)

Answer 1

cosx=V(1-(-5/13)²) = 
x = -5/13 ....... 3º Q 

V(1-25/169)= 

V(169-25)/13= 

V(144)/13= 

-12/13 

cosx=-12/13