Question
Find the derivative of the function $f(x) = \frac{{4x + 5\sin x}}{{3x + 7\cos x}}$

Answer

Here $f(x) = \frac{{4x + 5\sin x}}{{3x + 7\cos x}}$
$\therefore\;f'(x)=\frac{(3x+7\cos x)\frac d{dx}(4x+5\sin x)-(4x+5\sin x)\frac d{dx}(3x+7\cos x)}{{(3x+7\cos x)}^2}$
$ = \frac{{(3x + 7\cos x)(4+ 5\cos x) - (4x + 5\sin x)(3 - 7\sin x)}}{{{{(3x + 7\cos x)}^2}}}$
$=\;\frac{12x+15x\cos x+28\cos x+35\cos^2x-12x+28x\sin x-15\sin x+35\;\sin^2x}{{(3x+7\cos x)}^2}$
$ = \frac{{15x\cos x + 28\cos x + 28x\sin x - 15\sin x + 35({{\cos }^2}x + {{\sin }^2}x)}}{{{{(3x + 7\cos x)}^2}}}$
$ = \frac{{15x\cos x + 28\cos x + 28x\sin x - 15\sin x + 35}}{{{{(3x + 7\cos x)}^2}}}$

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