Find the points where the graph of the function has horizontal tangents.
f(x) = 6x^2 + 6x +5

The answer is supposed to be -1/2, 7/2; however, I'm not sure how to get 7/2?

I first found the derivative: 12x +6. Then, I factored out, which would simply be 12(x+1/2). Then I found the zero, which would only be -1/2.

Please help! Where does the 7/2 come from, and how do I find it? Thank you :)

Question

Find the points where the graph of the function has horizontal tangents.
f(x) = 6x^2 + 6x +5

The answer is supposed to be -1/2, 7/2; however, I'm not sure how to get 7/2?

I first found the derivative: 12x +6. Then, I factored out, which would simply be 12(x+1/2). Then I found the zero, which would only be -1/2.


Please help! Where does the 7/2 come from, and how do I find it? Thank you :)