For what values of x does the graph of f (x) have a horizontal tangent? (Round the answers to three decimal places.)

f (x) = 2x^3 + 6x^2 + 2 x + 9

horizontal tangent has a zero slope

so would i differentiate it before i set the equation =0?

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- September 26th 2009, 08:58 PMjayjay60horizontal tangent
For what values of x does the graph of f (x) have a horizontal tangent? (Round the answers to three decimal places.)

f (x) = 2x^3 + 6x^2 + 2 x + 9

horizontal tangent has a zero slope

so would i differentiate it before i set the equation =0? - September 26th 2009, 09:01 PMdifferentiate
yes, Differentiate first.

- September 26th 2009, 09:10 PMjayjay60
well i got 6x^2+12x+2, do i set this equal to 0 or what next? i've been studying math all day long. i'm f'serious. >.<,

- September 26th 2009, 09:49 PMdifferentiate
Yep set it to zero.

it becomes

and then find the values of x, using the quadratic formula or completing the square.

the answer becomes