Evaluate `int_(0)^(infty) e^(-2x)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)^(oo)e^(-x)dx

Evaluate int_(0)^(1)e^(2-3x)dx

Evaluate int_(0)^(1)e^(2-3x)dx

Evaluate : int_(0)^(4)x.e ^(2x) dx