$$ \int \frac{2 x+5}{\sqrt{7-6 x-x^2}} d x=A \sqrt{7-6 x-x^2}+B \sin ^{-1}\left(\frac{x+3}{4}\right)+C $$…

$$ \int \frac{2 x+5}{\sqrt{7-6 x-x^2}} d x=A \sqrt{7-6 x-x^2}+B \sin ^{-1}\left(\frac{x+3}{4}\right)+C $$ (where $C$ is a constant of integration), then the ordered pair $(A, B)$ is equal to
  1. $(-2,-1)$
  2. $(2,-1)$
  3. $(-2,1)$
  4. $(2,1)$

Solution

$\because 7-6 x-x^2=16-(x+3)^2$ and $\frac{d}{d x}\left(7-6 x-x^2\right)=-2 x-6$ So, $\int \frac{2 x+5}{\sqrt{7-6 x-x^2}} d x=\int \frac{2 x+6}{\sqrt{7-6 x-x^2}} d x$ $ -\int \frac{1}{\sqrt{16-(x+3)^2}} d x $ $ =-2 \sqrt{7-6 x-x^2}-\sin ^{-1}\left(\frac{x+3}{4}\right)+C $ Therefore, $A=-2, \& B=-1$

Asked in: JEE Main 2018 (15 Apr Shift 2 Online)

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