Question

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

Answer 1

HI!!

Answer 2

hey!

Answer 3

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!

Answer 4

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

Answer 5

you good from there?

Answer 6

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

Answer 7

yes

Answer 8

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

Answer 9

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

Answer 10

ok got it. the zeros are -3 and 4

Answer 11

thank you!!

Answer 12

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