Question

If cos9x-2cos6x=2,then the generel solution of x is

Answer 1

Answer:

Step-by-step explanation:

cos6x = 2 (cos3x) ^ 2 - 1  

cos9x = 4 (cos3x) ^ 3 - 3 (cos3x).  

Cos3x considered t = (| T | =  

==> 4T ^ 3 - 4T ^ 2 - 3T + 2 = 2  

==> T = 0;  

. T = -1/2  

. T = 3/2 (by type> 1)  

$ * $ With cos 3x = 0 ==> 3x = (Pi) / 2 + k (Pi) ==> x = (Pi) / 6 + k (Pi) / 3  

$ * $ With cos 3x = -1/2 ==> 3x = - (P) / 3 + k2 (Pi) ==> x = - (P) / 9 + k2 (Pi) / 3