JEE Challenger
More from Integrals

Periodicity of the Indefinite Integral of Sine Squared

Let F(x)F(x) be an indefinite integral of sin⁡2x\sin^2 x.

STATEMENT-1 : The function F(x)F(x) satisfies F(x+π)=F(x)F(x + \pi) = F(x) for all real xx.

because

STATEMENT-2 : sin⁡2(x+π)=sin⁡2x\sin^2(x + \pi) = \sin^2 x for all real xx.

Options

A

Statement-1 is True, Statement-2 is True; Statement-2 is a correct explanation for Statement-1

B

Statement-1 is True, Statement-2 is True; Statement-2 is NOT a correct explanation for Statement-1

C

Statement-1 is True, Statement-2 is False

D

Statement-1 is False, Statement-2 is True

Correct

Step-by-Step Solution

To determine the validity of the given statements, let us analyze each of them:

Evaluation of Statement-2:
We know the trigonometric identity:
sin⁡(x+π)=−sin⁡x\sin(x + \pi) = -\sin x
Squaring both sides gives:
sin⁡2(x+π)=(−sin⁡x)2=sin⁡2xfor all real x\sin^2(x + \pi) = (-\sin x)^2 = \sin^2 x \quad \text{for all real } x
Thus, sin⁡2x\sin^2 x is a periodic function with period π\pi.
Therefore, Statement-2 is True.

Evaluation of Statement-1:
Given that F(x)F(x) is an indefinite integral of sin⁡2x\sin^2 x, we have:
F(x)=∫sin⁡2x dx=∫1−cos⁡2x2 dx=x2−sin⁡2x4+CF(x) = \int \sin^2 x \, dx = \int \frac{1 - \cos 2x}{2} \, dx = \frac{x}{2} - \frac{\sin 2x}{4} + C
where CC is an arbitrary constant of integration.

Now, let us calculate F(x+π)F(x + \pi):
F(x+π)=x+π2−sin⁡(2(x+π))4+CF(x + \pi) = \frac{x + \pi}{2} - \frac{\sin(2(x + \pi))}{4} + C
F(x+π)=x2+π2−sin⁡(2x+2π)4+CF(x + \pi) = \frac{x}{2} + \frac{\pi}{2} - \frac{\sin(2x + 2\pi)}{4} + C
Since sin⁡(2x+2π)=sin⁡2x\sin(2x + 2\pi) = \sin 2x, this simplifies to:
F(x+π)=(x2−sin⁡2x4+C)+π2=F(x)+π2F(x + \pi) = \left(\frac{x}{2} - \frac{\sin 2x}{4} + C\right) + \frac{\pi}{2} = F(x) + \frac{\pi}{2}
Alternatively, by the Fundamental Theorem of Calculus:
F(x+π)−F(x)=∫xx+πsin⁡2t dt=π2≠0F(x + \pi) - F(x) = \int_{x}^{x + \pi} \sin^2 t \, dt = \frac{\pi}{2} \neq 0
Since F(x+π)=F(x)+π2≠F(x)F(x + \pi) = F(x) + \frac{\pi}{2} \neq F(x) for all real xx, F(x)F(x) is not periodic with period π\pi.
Therefore, Statement-1 is False.

Conclusion:
Statement-1 is False, and Statement-2 is True.

Hence, the correct option is (D).