Question

solve for x
cos(5x)+cos(2x)=0

Answer 1

use cosA+cosB identity

Answer 2

\[x = 2 (\pi n-\tan^(-1)(\sqrt(5/3-(2 (1+i \sqrt(3)))/(3 (1/14 (13+3 i \sqrt(3)))^(1/3))-1/3 2^(2/3) (1-i \sqrt(3)) (1/7 (13+3 i \sqrt(3)))^(1/3))))\]

Answer 3

i only know the identity of cos(A+B)

Answer 4

tell me what cos(A+B)+cos(A-B) is

Answer 5

so you mean B=0?

Answer 6

nope
just tell me what you get by using the formulae

Answer 7

cos(A)cos(B)-sin(A)sin(B)+cos(A)cos(B)+sin(A)sin(B)

Answer 8

=2cos(A)cos(B) right?

Answer 9

=> cos(5x)cos(2x)=0

Answer 10

no dont jump to conclusions
now put A+B=x and A-B=y

Answer 11

which means A=(x+y)/2 and B=(x-y)/2

Answer 12

now, what you get by cosx+cos y

Answer 13

why need the set A and x?

Answer 14

i am trying to get you to the formula. this x is not the x in the problem. instead its a general variable.

Answer 15

would you mind to give me all steps and lead it to the
answer Pi/7 + 4pi/7 k, 3pi/7+ 4pi/7 k, pi/3 + 4pi/3 k

Answer 16

x=pi/3