Can anyone please show me how to do 2cos2x=7cosx. I have no clue. Thanx in advance.
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Originally Posted by xwrathbringerx Can anyone please show me how to do 2cos2x=7cosx. I have no clue. Thanx in advance. $\displaystyle 2 \left( 2 \cos^2 (x) - 1 \right) = 7 \cos (x)$. Now re-arrange into a quadratic in cos x .....
cos2x=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
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