Trigonometry Help Please!

G'day,

One way:

Rewrite 2tanx as \(\displaystyle \frac{2\sin{x}}{\cos{x}}\)

Multiply through by cosx.

Rewrite \(\displaystyle \cos^2{x}\) as \(\displaystyle 1 - \sin^2{x}\).

Solve the quadratic -you may find it easier to let sinx = t, and solve for t using the quadratic formula, then relate back to x.

Then get (cosx)^2 from there.
 
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