What is the second derivative of y = lnx^2y=lnx2?

1 Answer
Aug 1, 2016

For the first derivative, use the chain rule.

y = ln(u)y=ln(u) and u = x^2u=x2. Then y' = 1/u and u' = 2x.

y' = 2x xx 1/u = 2x xx 1/(x^2) = (2x)/x^2

So, the first derivative is (2x)/x^2. The second derivative can be determined by differentiating the first.

By the quotient rule:

Let y = (g(x))/(h(x)), so that g(x) = 2x and h(x) = x^2. The derivative is given by y' = (g'(x) xx h(x) - g(x) xx h'(x))/(h(x))^2

The derivative of g(x) is 2 and the derivative of h(x) is 2x.

We can now substitute into the formula and calculate. Note: the notation y'' is used to show that we're finding the second derivative, and not the first, as would the notation y'. Similarly, y''' would signify the third derivative.

y'' = (2 xx x^2 -2x xx 2x)/(x^2)^2

y'' = (2x^2 - 4x^2)/x^4

y'' = (-2x^2)/x^4

y'' = -2/x^2

Hence, the second derivative is y'' = -2/x^2.

Hopefully this helps!