cos ⁡7x- cos ⁡8x1+2 cos ⁡5x dx=

Question

Accepted Answer

Correct answer: B. (b) Let ,I= cos ⁡7x- cos ⁡8x1+2 cos ⁡5x dx= cos ⁡7x- cos ⁡8x1+2-4 sin^2 ⁡ ( 5x2 ) dx= 2 sin ⁡ 15x2 sin ⁡ x23-4 sin^2 ⁡ ( 5x2 ) dx= 2 sin ⁡ 15x2 sin ⁡ x2 sin ⁡ 5x23 sin ⁡ 5x2-4 sin^3 ⁡ 5x2 dx= 2 sin ⁡ 15x2 sin ⁡ x2 sin ⁡ 5x2 sin ⁡ 15x2 dx= 2 sin ⁡ x2 sin ⁡ 5x2 dx= cos ⁡2x- cos ⁡3 xdx= 12 sin ⁡2x- 13 sin ⁡3x+c ( ∵ sin ⁡3 =3 sin ⁡ -4 sin^3 ⁡ )

$\sum \frac{cos 7 x - cos 8 x}{1 + 2 cos 5 x} dx =$

Solution

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