If $g(x)=\int_0^x \cos 4 t ~d t$, then $g(x+\pi)$ equals

If $g(x)=\int_0^x \cos 4 t ~d t$, then $g(x+\pi)$ equals
  1. $\frac{g(x)}{g(\pi)}$
  2. $g(x)+g(\pi)$
  3. $g(x)-g(\pi)$
  4. None of these

Solution

$g(x)=\int_0^x \cos 4 t ~d t$ $\Rightarrow g^{\prime}(x)=\cos 4 x \quad \Rightarrow g(x)=\frac{\sin 4 x}{4}+k \quad \Rightarrow g(x)=\frac{\sin 4 x}{4}[\because g(0)=0]$ $g(x+\pi)=g(x)+g(\pi)=g(x)-g(\pi)(\because g(\pi)=0)$

Asked in: JEE Main 2012 (Offline)

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