# Implicit Differentiation: find the derivative of the function at the indicated point. lnxy+5x=30 at (1, e^25).I have figured the following so far: (1/xy)+5x(dy/dx)=0 I think that is how it goes.

### 1 Answer | Add Yours

You need to find `(dy)/(dx)` for the given function, hence, you need to differentiate with respect to x such that:

`(d(ln xy))/(dx) + (d(5x))/(dx) = (d(30))/(dx)`

`1/(xy)*(y + x*(dy)/(dx)) + 5 = 0`

You need to open the brackets such that:

`y/(xy) + (x/(xy))*(dy)/(dx) = -5`

`1/x + (1/y)*(dy)/(dx) = -5 => (1/y)*(dy)/(dx) = -5 - 1/x => (dy)/(dx) =y(-5 - 1/x)`

You need to evaluate `(dy)/(dx)` at `(1,e^25)` such that:

`(dy)/(dx) =e^25(-5 - 1/1) =>(dy)/(dx) = -6*e^25`

**Hence, evaluating `(dy)/(dx)` at the given point yields `(dy)/(dx) = -6*e^25.` **