Question

If Cosx = 1/4
then the value of Cos 3x=?
a)11/16
b)-11/16
c)16/11
d)-16/11​

Answer 1

Answer:

b)-11/16

Step-by-step explanation:

Given Cosx = 1/4

cos 3A = 4 cos³A - 3cosA

hence

cos 3x = 4 cos³x - 3 cosx

           = 4 (1/4)³ - 3 (1/4)

           = ( 1/16) - (3/4)

           = (1-12)/16

           = -11/16