Let f(x)=∫ex(x−1)(x−2)dx , then f decreases in the inverval
−∞,−2
−2,−1
1,2
2,∞
f(x)=∫ex(x−1)(x−2)dx f'x=ex(x−1)(x−2) <0⇒x∈1,2
since f(x) is decreasing function ⇒f'(x)<0