# Thread: find where the tangent line is horizontal or vertical

1. ## find where the tangent line is horizontal or vertical

a) if x^3 + y^3 -xy^2 =5 , find dy/dx

b) find all points where the tangent line is horizontal or vertical

I was able to do the first part, and I got dy/dx = -3x^2 +y^2/3y^2-2xy.

However, I'm having some problems finding where the tangent line is either horizontal or vertical....... can I get some help.Thanks in advance

2. What does it mean for the tangent line to be horizontal. You know how to take derivatives, so you should know by this point that the derivative evaluated at zero, is where the curve has a horizontal tangent.

A vertical tangent (funny) occurs where the equation that defines the derivative does not exist.