# Evaluate $\large \int \frac{2\sin 2 x -\cos x }{6-\cos^2x -4\sin x }$$dx. ## 1 Answer Toolbox: • I=\int f(x) dx • Put x=g(t) then dx=g'(t) • Therefore I=\int f(g(t))g'(t)dt • \int \large\frac{dx}{x^+a^2}=\frac{1}{a}$$\tan^{-1}\big(\Large\frac{x}{a}\big)$
• $\int \large\frac{dx}{x}$$=\log \mid x\mid+c Step 1: Let I = \int \large\frac{ (2\sin2x - \cos x)}{(6-\cos^2x-4\sin x)}$$dx$
We know that $\sin 2x=2\sin x\cos x$
$\qquad=\int\large\frac {[4\sin x\cos x - \cos x] dx}{6-1+\sin^2x-4\sin x}$
$\qquad=\int \large\frac{ [\cos x(4\sin x-1)]dx}{[\sin^2x-4\sin x+5]}$
Step 2:
Put $\sin x = t$ then $\cos xdx = dt$
substituting this we get,
$\qquad=\int \large\frac{ [4t-1]dt}{t^2-4t+5}$
$\qquad=\int \large\frac{[4t-8+7]dt}{t^2-4t+5}$
$\qquad=\int 2 \large\frac{[2t-4]dt}{[t^2-4t+5]} +\frac{7dt}{[t^2-4t+5]}$
Step 3:
Put $t^2-4t+5= y$, then $[2t-4]dt = dy$
Therefore $\int 2 \large\frac{ dy}{y }$$+7 \int \large\frac{dt}{(t-2)^2+1} Step 4: On integrating we get, 2 \log |y| + 7 \tan^{-1}(t-2)$$+C$
Step 5:
Substituting for $y$ and $t$ we get