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