Give all radian solutions to

The only place where i know where to begin is

would i need to reduce the cos(7x) like

until i get down to cos(2x)?

so i could use the identity

Can anyone help me get started on this beast?

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- Aug 20th 2013, 11:36 PMicelatedsolving a trig problem
Give all radian solutions to

The only place where i know where to begin is

would i need to reduce the cos(7x) like

until i get down to cos(2x)?

so i could use the identity

Can anyone help me get started on this beast? - Aug 20th 2013, 11:43 PMibduttRe: solving a trig problem
Remember the identity cos ( A-B) = cos A cos B + sin A sin B use it and we have cos 5x = 1/2 now you can complete the solution.

- Aug 20th 2013, 11:50 PMicelatedRe: solving a trig problem
would i then use cos(5x) = cos(3x + 2x) is that the way to go?

or would i use arccos?

5x = arccos(1/2) - Aug 21st 2013, 01:00 AMibduttRe: solving a trig problem
No as mentioned the identity is cos ( A-B) = cos A cos B + sin A sin B

What we have is

LHS = cos(7x)cos(2x) + sin(7x)sin(2x) = cos ( 7x - 2x ) = cos 5X

thus we get cos 5x = 1/2