Question

Find all values of x (if any) where the tangent line to the graph of the given equation is horizontal. HINT [The tangent line is horizontal when its slope is zero.] (If an answer does not exist, enter DNE. Enter your answers as a comma-separated list.) y = −9x2 − 8x

Answer 1

Do you know how to take the derivative of this?

Answer 2

no

Answer 3

Have you been shown derivatives at all?

Answer 4

Given that it's a quadratic, I think you can get by without derivatives.
Just think about where, for a quadratic, the tangent line would be horizontal. (Although, it does seem like an odd question to have in a class where derivatives haven't been covered)