Skip to main content
Back to Indefinite Integration
JEE Main 2022
Indefinite Integration
Indefinite Integrals
Hard

Question

For I(x)=sec2x2022sin2022xdxI(x)=\int \frac{\sec ^{2} x-2022}{\sin ^{2022} x} d x, if I(π4)=21011I\left(\frac{\pi}{4}\right)=2^{1011}, then

Options

Solution

Key Concepts and Formulas

  • Integration by parts: udv=uvvdu\int u \, dv = uv - \int v \, du
  • Trigonometric identities: secx=1cosx\sec x = \frac{1}{\cos x}, tanx=sinxcosx\tan x = \frac{\sin x}{\cos x}
  • Power rule for exponents: aman=amn\frac{a^m}{a^n} = a^{m-n}

Step-by-Step Solution

Step 1: Rewrite the integral and prepare for integration by parts. We are given the integral I(x)=sec2x2022sin2022xdx=sec2xsin2022xdx2022sin2022xdxI(x) = \int \frac{\sec^2 x - 2022}{\sin^{2022} x} dx = \int \frac{\sec^2 x}{\sin^{2022} x} dx - \int \frac{2022}{\sin^{2022} x} dx We aim to use integration by parts on the first integral.

Step 2: Apply integration by parts to the first integral. Let u=1sin2022xu = \frac{1}{\sin^{2022} x} and dv=sec2xdxdv = \sec^2 x \, dx. Then du=2022cosxsin2023xdxdu = \frac{-2022 \cos x}{\sin^{2023} x} dx and v=tanxv = \tan x. Applying integration by parts, we have sec2xsin2022xdx=tanxsin2022xtanx2022cosxsin2023xdx=tanxsin2022x+2022sinxcosxcosxsin2023xdx\int \frac{\sec^2 x}{\sin^{2022} x} dx = \frac{\tan x}{\sin^{2022} x} - \int \tan x \cdot \frac{-2022 \cos x}{\sin^{2023} x} dx = \frac{\tan x}{\sin^{2022} x} + \int \frac{2022 \sin x}{\cos x} \cdot \frac{\cos x}{\sin^{2023} x} dx =tanxsin2022x+2022sin2022xdx= \frac{\tan x}{\sin^{2022} x} + \int \frac{2022}{\sin^{2022} x} dx

Step 3: Substitute the result back into the original integral. Substituting this back into the original integral, we get I(x)=tanxsin2022x+2022sin2022xdx2022sin2022xdx=tanxsin2022x+CI(x) = \frac{\tan x}{\sin^{2022} x} + \int \frac{2022}{\sin^{2022} x} dx - \int \frac{2022}{\sin^{2022} x} dx = \frac{\tan x}{\sin^{2022} x} + C

Step 4: Determine the constant of integration using the given condition. We are given that I(π4)=21011I\left(\frac{\pi}{4}\right) = 2^{1011}. Thus, 21011=tan(π/4)sin2022(π/4)+C=1(1/2)2022+C=(2)2022+C=(21/2)2022+C=21011+C2^{1011} = \frac{\tan(\pi/4)}{\sin^{2022}(\pi/4)} + C = \frac{1}{(1/\sqrt{2})^{2022}} + C = (\sqrt{2})^{2022} + C = (2^{1/2})^{2022} + C = 2^{1011} + C Therefore, C=0C = 0.

Step 5: Write the final expression for I(x)I(x). I(x)=tanxsin2022xI(x) = \frac{\tan x}{\sin^{2022} x}

Step 6: Evaluate I(π/3)I(\pi/3) and I(π/6)I(\pi/6). I(π3)=tan(π/3)sin2022(π/3)=3(3/2)2022=3(3)2022/22022=32202231011I\left(\frac{\pi}{3}\right) = \frac{\tan(\pi/3)}{\sin^{2022}(\pi/3)} = \frac{\sqrt{3}}{(\sqrt{3}/2)^{2022}} = \frac{\sqrt{3}}{(\sqrt{3})^{2022}/2^{2022}} = \frac{\sqrt{3} \cdot 2^{2022}}{3^{1011}} I(π6)=tan(π/6)sin2022(π/6)=1/3(1/2)2022=220223I\left(\frac{\pi}{6}\right) = \frac{\tan(\pi/6)}{\sin^{2022}(\pi/6)} = \frac{1/\sqrt{3}}{(1/2)^{2022}} = \frac{2^{2022}}{\sqrt{3}}

Step 7: Check option (A). 31010I(π3)I(π6)=3101032202231011220223=322022331010220223=220223220223=03^{1010} I\left(\frac{\pi}{3}\right) - I\left(\frac{\pi}{6}\right) = 3^{1010} \cdot \frac{\sqrt{3} \cdot 2^{2022}}{3^{1011}} - \frac{2^{2022}}{\sqrt{3}} = \frac{\sqrt{3} \cdot 2^{2022}}{3} \cdot 3^{1010} - \frac{2^{2022}}{\sqrt{3}} = \frac{2^{2022}}{\sqrt{3}} - \frac{2^{2022}}{\sqrt{3}} = 0 Thus, option (A) is correct.

Step 8: Briefly check option (B). 31010I(π6)I(π3)=3101022022332202231011=3101022022322022303^{1010} I\left(\frac{\pi}{6}\right) - I\left(\frac{\pi}{3}\right) = 3^{1010} \cdot \frac{2^{2022}}{\sqrt{3}} - \frac{\sqrt{3} \cdot 2^{2022}}{3^{1011}} = \frac{3^{1010} \cdot 2^{2022}}{\sqrt{3}} - \frac{2^{2022}}{\sqrt{3}} \neq 0

Common Mistakes & Tips

  • Remember to include the constant of integration, CC, when evaluating indefinite integrals.
  • Be careful with trigonometric identities and simplifying expressions.
  • Double-check the integration by parts steps to avoid errors in the derivative and integral.

Summary

We first evaluated the indefinite integral I(x)I(x) using integration by parts. We then used the given condition I(π/4)=21011I(\pi/4) = 2^{1011} to find the constant of integration. Finally, we evaluated I(π/3)I(\pi/3) and I(π/6)I(\pi/6) and substituted them into the options to find the correct answer.

Final Answer

The final answer is \boxed{0}, which corresponds to option (A).

Practice More Indefinite Integration Questions

View All Questions