How do you differentiate #f(x)=sqrt(e^(5x^2+x+3) # using the chain rule?

1 Answer
Jul 10, 2016

This will require the application of the chain rule--twice.

First, for #e^(5x^2 + x + 3)#

Let #y = e^u#, and #u = 5x^2 + x + 3#

#dy/dx = dy/(du) xx (du)/dx#

The derivative of #e^u# is #e^u#. The derivative of #5x^2 + x + 3# is #10x + 1#.

Hence,

#dy/dx = e^u xx 10x + 1#

#dy/dx = (10x + 1)e^(5x^2 + x + 3)#

Now for the second application of the chain rule.

Let #y = sqrt(u) = u^(1/2)# and #u = e^(5x^2 + x + 3)#

We already know the derivative of #u#. The derivative of #y#, by the power rule, is #1/2u^(-1/2) = 1/(2u^(1/2))#.

Hence,

#dy/dx = 1/(2u^(1/2)) xx (10x + 1)e^(5x^2 + x + 3)#

#dy/dx = ((10x + 1)e^(5x^2 + x + 3))/(2sqrt(e^(5x^2 + x + 3))#

#f'(x) = ((10x + 1)e^(5x^2 + x + 3))/(2sqrt(e^(5x^2 + x + 3))#

#f'(x) = ((10x + 1)e^(5x^2 + x + 3))/(2(e^(5x^2 + x + 3))^(1/2)#

By the quotient rule of exponents: #a^n/a^m = a^(n - m)#:

#f'(x) = ((10x + 1)sqrt(e^(5x^2 + x + 3)))/2#

Hopefully this helps!