Question

How do you find the points where the graph of the function `y = 9 + 9x` has horizontal tangents?

Answer 1

There are no such points.

Explanation:

`y=9+9x`

You can see that this is a straight line of the form `y=mx+c` so no calculus is needed. It is a straight line of gradient 9 and intercept 9:

graph{9+9x [-10, 10, -5, 5]}

There can be no horizontal tangents.