Question

What are the coordinates of the vertex of the graph of the function y = -3x^2 - 12x + 3?
a.) (-2, 29)
b.) (2, -15)
c.) (2, -9)
d.) (-2, 15)
I think it might be B, but I'm not sure.

Answer 1

did you draw the graph

Answer 2

the x-value of the graph of a parabola, form ax^2+bx+c is -b/2a. If you then plug that x-value in, you get the y-value of the vertex.

Answer 3

here, -b/2a=-(-12)/2(-3) --> 12/-6 = -2
y evaluated at x=-2 gives:
y=-3(4)-12(-2)+3=-12+24+3=15
So, your answer is (-2, 15). It is D; you were close, though.

Answer 4

I think its -2,15 because if im not wrong it has to be -2

Answer 5

change it to vertex form.
\[y= -3x ^{2}-12x+3\]
\[y=-3(x ^{2}+4x-1)\]
\[y=-3[(x ^{2}+4x+4)-1-4]\]
\[y=-3[(x+2) ^{2}-5]\]
\[y=-3(x+2) ^{2}+15\]
so vertex is (-2,15)

Answer 6

btw,
\[y=a(x-h) ^{2}+k\] where vertex is (h,k)

Answer 7

I don't think I learned the vertex form !!! I hate teachers who don't know how to teach !!!

Answer 8

oh if you did not, you will later.
you can use \[-\frac{ b }{ 2a }\] to find the x coordinate of the vertex, the find the y coordinate by inserting the answer for x.

Answer 9

that was what I learned before the vertex form in algebra.

Answer 10

so exactly what I said...?

Answer 11

yep

Answer 12

you should use the Equation form, it is easier to read.

Answer 13

I know. I don't feel like taking the time sometimes.