Can anyone please show me how to do 2cos2x=7cosx. I have no clue.

Thanx in advance.

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- Oct 2nd 2008, 04:36 AMxwrathbringerxTrig Equation
Can anyone please show me how to do 2cos2x=7cosx. I have no clue.

Thanx in advance. - Oct 2nd 2008, 04:52 AMmr fantastic
- Oct 2nd 2008, 10:32 AMdolphinlover
cos2

*x*=2(cos^2)*x-1 (double angle)...*that is how Mr Fantastic got his result.

Rearranging into a quadratic in cos x should yield...

(4cosx +1)(cosx -2) = 0

(4cosx) + 1 = 0 and

(cosx) - 2 = 0

....now solve for x in both