What is the equation of the normal line of #f(x)=x/lnx# at #x=4 #?
First of all, we need a point of intersection. We know the line will intersect
So we know at least
Next we need the gradient of the line and this is obtained by taking the derivative of
Thus we have the gradient of the line.
Now substitute into the formula:
We can better visualise this from the graphs of the function: