How do you differentiate f(x) = x^2 sqrt((x+1)/(x^2+1))?

1 Answer
Apr 23, 2016

f'(x)=(x^2)(((x^2+1)^(1/2)(1/(2sqrt(x+1)))-(x+1)^(1/2)((x)/(sqrt(x^2+1))))/(x^2+1)) + (2x)(sqrt((x+1)/(x^2+1)))

Explanation:

For this problem, we will need a combination of chain rule, product rule, quotient rule, and power rule...Yuck.

f'(x)=(x^2)(sqrt((x+1)/(x^2+1)))' + (2x)(sqrt((x+1)/(x^2+1)))

Notice the little apostrophe tagging along the first sqrt((x+1)/(x^2+1)? That means we still need to find the derivative of that part. Start off with chain rule...

1/(2sqrt((x+1)/(x^2+1))) * (((x+1)^(1/2))/(x^2+1)^(1/2))

The first part of the above looks good. Now let's focus on the last part. Using quotient rule...

((x^2+1)^(1/2)(1/(2sqrt(x+1)))-(x+1)^(1/2)((x)/(sqrt(x^2+1))))/(x^2+1)

Dang...I would like to see anyone simplify this...your answer , by the way, is

f'(x)=(x^2)(((x^2+1)^(1/2)(1/(2sqrt(x+1)))-(x+1)^(1/2)((x)/(sqrt(x^2+1))))/(x^2+1)) + (2x)(sqrt((x+1)/(x^2+1)))

Many apologies that I can't go any further into this problem. This is certainly a mammoth...just hope that something like this doesn't appear on your tests. :)