How do you integrate (x^5)*(e^(x^2/2))(x5)(ex22)?

1 Answer
Sep 1, 2015

(4x^4-4x^2-8)e^(x^2/2)+c(4x44x28)ex22+c

Explanation:

Let's assume x^2/2 = tx22=t
=> (2xdx)/2 = t, x dx = dt2xdx2=t,xdx=dt

=int(x^5)*(e^(x^2/2))dx=(x5)(ex22)dx can be written as,

=int(x^2)(x^2)x(e^(x^2/2))dx=(x2)(x2)x(ex22)dx

Substituting with tt we get

=int(2t)(2t)(e^t)dt=(2t)(2t)(et)dt

=4intt^2(e^t)dt=4t2(et)dt

Using Integration by Parts,

∫(I)(II)dx=(I)∫(II)dx−∫((I)'∫(II)dx)dx

where (I) and (II) are functions of x, and (I) represents which will be differentiated and (II) will be integrated subsequently in the above formula

Similarly following for the problem,

=4(t^2)inte^tdt-4int((t^2)'inte^tdt)dt+c

=4t^2e^t-4int2te^tdt+c

=4t^2e^t-8intte^tdt+c

Applying again integration by parts in second term, we get

=4t^2e^t-8(te^t-inte^tdt)+c

=4t^2e^t-8(te^t-e^t)+c

=4t^2e^t-8te^t-8e^t+c

Substituting t back,

=4(x^2/2)^2e^(x^2/2)-8(x^2/2)e^(x^2/2)-8e^(x^2/2)+c, where c is a constant

=(4x^4-4x^2-8)e^(x^2/2)+c