Q91 / 150 · MHT CET 2026 (13 April Shift 2) · Mathematics
If $\int x^2 \cdot e^x dx = e^x f(x) + c$, then the minimum value of $f(x)$ is ...
- A$0$
- B$-1$
- Correct answerC$1$
- D$\dfrac{-1}{4}$
Solution
Using integration by parts:
$\int x^2 e^x dx = x^2 e^x - \int 2x e^x dx$
$= x^2 e^x - 2(x e^x - \int e^x dx)$
$= x^2 e^x - 2x e^x + 2e^x + c$
$= e^x (x^2 - 2x + 2) + c$
Comparing with the given expression, we get $f(x) = x^2 - 2x + 2$.
To find the minimum value of $f(x)$, we can complete the square:
$f(x) = (x - 1)^2 + 1$
Since $(x - 1)^2 \geq 0$ for all real $x$, the minimum value of $f(x)$ is $1$.
Answer: $1$
$\int x^2 e^x dx = x^2 e^x - \int 2x e^x dx$
$= x^2 e^x - 2(x e^x - \int e^x dx)$
$= x^2 e^x - 2x e^x + 2e^x + c$
$= e^x (x^2 - 2x + 2) + c$
Comparing with the given expression, we get $f(x) = x^2 - 2x + 2$.
To find the minimum value of $f(x)$, we can complete the square:
$f(x) = (x - 1)^2 + 1$
Since $(x - 1)^2 \geq 0$ for all real $x$, the minimum value of $f(x)$ is $1$.
Answer: $1$
Hence, the correct answer is option: 'C'.