∫ ƒ(x) dx = xe^(- x²)
ƒ(x) = (1 - 2x²)e^(- x²)
ƒ'(x) = 2x(2x² - 3)e^(- x²)
∫ ƒ'(x)ƒ''(x) dx
= ∫ ƒ'(x) d[ƒ'(x)]
= (1/2)[ƒ'(x)]² + C
= (1/2)[2x(2x² - 3)e^(- x²)]² + C
= 2x²(2x² - 3)²e^(- 2x²) + C