JEE 2023 — Mathematics PYQ
JEE | Mathematics | 2023∫0∞e3x+6e2x+11ex+66dx
Choose the correct answer:
- A.
loge(2732)
(Correct Answer) - B.
loge(81256)
loge(2732)
Explanation
Let I=∫0∞e3x+6e2x+11ex+66dx
I=∫0∞(ex+1)(ex+2)(ex+3)6 dx (on factorising the Dr)
Let (ex+1)(ex+2)(ex+3)6=ex+1A+ex+2B+ex+3C
On solving, we get A=3, B=−6, C=3
so I=∫0∞ex+13dx−∫0∞ex+26dx+∫0∞ex+33dx
=3∫0∞1+e−xe−xdx−6∫0∞1+2e−xe−xdx+3∫0∞1+3e−xe−xdx
=−3[log(1+e−x)]0∞+6×21[log(1+2e−x)]0∞−3×31[log(1+3e−x)]0∞
=−3(0−log2)+3(0−log3)−(0−log4)
=3log2−3log3+log4
=log3323×4=log2732
Explanation
Let I=∫0∞e3x+6e2x+11ex+66dx
I=∫0∞(ex+1)(ex+2)(ex+3)6 dx (on factorising the Dr)
Let (ex+1)(ex+2)(ex+3)6=ex+1A+ex+2B+ex+3C
On solving, we get A=3, B=−6, C=3
so I=∫0∞ex+13dx−∫0∞ex+26dx+∫0∞ex+33dx
=3∫0∞1+e−xe−xdx−6∫0∞1+2e−xe−xdx+3∫0∞1+3e−xe−xdx
=−3[log(1+e−x)]0∞+6×21[log(1+2e−x)]0∞−3×31[log(1+3e−x)]0∞
=−3(0−log2)+3(0−log3)−(0−log4)
=3log2−3log3+log4
=log3323×4=log2732

