Evaluate `int_(0)^(infty) [2/e^x]dx`

Evaluate int_(0)^(infty) e^(-x)x^(3)dx .

The value of int_(0)^(infty)[2e^(-x)] dx (where ,[.] denotes the greatest integer function of x) is equal to S

" Evaluate "int_(0)^(t)x^(2)e^(-x)dx

Evaluate int_(0)^(2)e^(x)dx

Evaluate int_(0)^(2)e^(2)dx

Evaluate : int_0^(ln2)x e^(-x)dx

Evaluate int_0^1 e^(2x) dx