For what value(s) of x does the graph of
f(x)=2x^3−3x^2−72x
have a horizontal tangent?

Question

For what value(s) of x does the graph of
f(x)=2x^3−3x^2−72x
have a horizontal tangent?

misty1212 · Answer

HI!!

anonymous · Answer

hey!

misty1212 · Answer

you are being asked where the derivative is zero
you have a cubic function
the derivative will be a quadratic function 
find the zeros of the quadratic!

misty1212 · Answer

if you are lucky it factors
if not, use the quadratic formula

misty1212 · Answer

you good from there?

anonymous · Answer

is the derivative f'(x) = 6x^2 -6x -72?

misty1212 · Answer

yes

misty1212 · Answer

factor out the 6, then it will be easier to factor what is left

misty1212 · Answer

it is kind of cute
when you take elementary algebra they teach you how to find the zeros using the quadratic formula, but when you take calculus all the questions are cooked up so you can factor and find the zeros

anonymous · Answer

ok got it. the zeros are -3 and 4

anonymous · Answer

thank you!!

misty1212 · Answer

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