How do I evaluate d/dx \int_5^(x^4) \sqrt{t^2 + t} dtddxx45t2+tdt?

2 Answers

To solve d /dx \int_5^{x^4} sqrt{t^2+t} dtddxx45t2+tdt, we will use the Fundamental Theorem of Calculus.

d /dx \int_5^{x^4} sqrt{t^2+t} dtddxx45t2+tdt
= [\sqrt{(x^4)^2+x^4}] * (4x^3)=[(x4)2+x4](4x3) **don't forget to chain!!

Mar 6, 2017

= 4x^5 \ sqrt(x^4 + 1)

Explanation:

The FTC tells us that, for constant a and parameter u:

d/(du) int_a^u f(t) dt = f(u)

Now for the chaining bit.

If in fact u = u(x), we can say that:

d/(dcolor(red)(x)) int_a^(u(x)) f(t) dt

= d/(du) (int_a^(u) f(t) dt ) cdot (du)/(dx)

= f(u) cdot (du)/dx

So for the specific question, where u(x) = x^4:

d/(dx) int_5^(x^4) sqrt(t^2 + t) \ dt

= sqrt((x^4)^2 + x^4) cdot d/dx (x^4)

= x^2\ sqrt(x^4 + 1) cdot 4x^3

= 4x^5 \ sqrt(x^4 + 1)