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Q.∫2x+2 dx\int 2^{x+2}\, dx is equal to :

(a) 2x+2+C2^{x+2} + C
(b) 2x+2log⁡2+C2^{x+2} \log 2 + C
(c) 2x+2log⁡2+C\frac{2^{x+2}}{\log 2} + C
(d) 2⋅2xlog⁡2+C2 \cdot \frac{2^x}{\log 2} + C
CBSECBSE Class XII Board 2023MCQ· 1mImportance★★★★★
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Exponential integrals with base aa follow the pattern ∫ax dx=axln⁡a+C\int a^x \, dx = \frac{a^x}{\ln a} + C. Rewriting 2x+2=4⋅2x2^{x+2} = 4 \cdot 2^x and integrating gives 2x+2log⁡2+C\frac{2^{x+2}}{\log 2} + C.

The heart of this problem is understanding how exponential functions integrate when the base isn't ee. We're comfortable with ∫ex dx=ex+C\int e^x \, dx = e^x + C because ee is special—it's its own derivative. But what happens when we have a different base like 22?

The key insight is that any exponential axa^x can be rewritten using the natural exponential: ax=exln⁡aa^x = e^{x \ln a}. This connection lets us integrate any exponential function by relating it back to exe^x.

∫ax dx=axln⁡a+C\int a^x \, dx = \frac{a^x}{\ln a} + C

This formula comes from the chain rule in reverse. When we differentiate axa^x, we get axln⁡aa^x \ln a, so when we integrate, we must divide by that same factor ln⁡a\ln a.

Now let's work through the given integral step by step.

  1. Simplify the exponent using exponential laws The expression 2x+22^{x+2} can be rewritten as:

2x+2=2x⋅22=4⋅2x2^{x+2} = 2^x \cdot 2^2 = 4 \cdot 2^x

This factorization pulls out the constant multiplier, making the integral cleaner.

  1. Pull the constant outside the integral

∫2x+2 dx=∫4⋅2x dx=4∫2x dx\int 2^{x+2} \, dx = \int 4 \cdot 2^x \, dx = 4 \int 2^x \, dx

  1. Apply the exponential integration formula Using our formula with a=2a = 2: 4∫2x dx=4⋅2xln⁡2+C=4⋅2xln⁡2+C4 \int 2^x \, dx = 4 \cdot \frac{2^x}{\ln 2} + C = \frac{4 \cdot 2^x}{\ln 2} + C …

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