1.

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

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 cosecx dx + ∫ cot2 x (cosecx 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 = ∫ cosecx dx + 2 ∫ cosec2 x cot2 x dx + ∫ cotx 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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