Question

Find all values of x (if any) where the tangent line to the graph of the given equation is horizontal. HINT [The tangent line is horizontal when its slope is zero.] (If an answer does not exist, enter DNE. Enter your answers as a comma-separated list.)

y = −9x2 − 8x

x = ___________

Answer 1

this is a parabola opening downwards. so the tangent line will be horizontal at the vertex. find the vertex.

or you can take the derivative and set that to 0. whatever way is easier for you do it...

Answer 2

so would the derivative = -18x - 8

Answer 3

yes...

Answer 4

x = ??? you there?

Answer 5

x = -8

Answer 6

set your derivative to 0:
-18x - 8 = 0

try again...

Answer 7

x= -8/18 or 0.44444

Answer 8

ok. the fractional answer is better (i think...) and you can reduce that to -4/9

Answer 9

u god?

Answer 10

thank you :)

Answer 11

u good?

Answer 12

i wish i was god

Answer 13

yw.

Answer 14

sorry, me too... :)