Question

solve cosx+cos2x+cos3x=0​

Answer 1

Answer:

cosx+cos3x+cos2x=0

cosx+cos3x=2cos2xcosx

2cos2xcosx+cos2x=0

cos2x(2cosx+1)=0

when cos2x=0

x=(2n+1)pay/2

when2cosx+1=0

2cosx=-1

cosx=-1/2=(pay-pay/3)

=2pay/3

then x=2npay+2pay/3