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The value of ∫ cosec6 x dx will be ___________, where c is an arbitrary constant.1. \(\frac {-1}5 \cot^5x-\frac 2 3 \cot^3 x - \cot x + c\)2. -sin7 x - 5 sin5 x - 3 sin3 x - sin x + c3. cos5 x + 3 cos3 x + cos x + c4. cos6 x - 4 cos4 x + 2 cos2 x + c |
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Answer» Correct Answer - Option 1 : \(\frac {-1}5 \cot^5x-\frac 2 3 \cot^3 x - \cot x + c\) I = ∫ cosec6 x dx I = ∫ cosec4 x cosec2 x dx We know that: cosec2 x = 1 + cot2 x I = ∫ cosec4 x (1 + cot2 x) dx I = ∫ cosec4 x dx + ∫ cot2 x cosec4 x dx I = ∫ cosec2 x cosec2 x dx + ∫ cot2 x (cosec2 x cosec2 x) dx I = ∫ cosec2 x (1 + cot2 x) dx + ∫ cot2 x cosec2x (1 + cot2 x) dx I = ∫ cosec2 x dx + ∫ cosec2 x cot2 x dx + ∫ cot2 x cosec2 x + ∫ cot4 x cosec2 x dx I = ∫ cosec2 x dx + 2 ∫ cosec2 x cot2 x dx + ∫ cot4 x cosec2 x dx Put cot x = z By differentiating we have, - cosec2 x dx = dz I = ∫ (- dz) + 2 ∫ z2 (- dz) + ∫ z4 (- dz) \(I~=~-~z~-~\frac{2z^3}{3}~-~\frac{z^5}{5}~+~c\) Put z = cot x in above equation: \(I~=~-~cot~x~-~\frac{2cot^3~x}{3}~-~\frac{cot^5~x}{5}~+~c\) \(I~=~\frac {-1}5 \cot^5x-\frac 2 3 \cot^3 x - \cot x + c\) |
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