Question

Determine whether the graph of y = x2 + 2x − 8 has a maximum or minimum point, then find the maximum or minimum value.

Maximum; (-1, -9)
Minimum; (-1, -9)
Maximum; (-9, -1)
Minimum; (-9, -1)

Answer 1

Is this a parabola that opens UP or DOWN...?

Answer 2

I think it opens up I"m not sure though.

Answer 3

You are correct...as long as that leading number (1x^2) is positive *as it is* the parabola opens up...and SINCE it opens up...



We have a minimum point right?

Answer 4

yes.

Answer 5

Now we want to find the vertex of the parabola....so we will use the equation

\[\large Vertex = \frac{ -b }{ 2a }\]

Remember your equation is in the form

\[\large ax^2 + bx + c\]

So your 'b' value is 2....and your 'a' value is just 1 right?...so we have

\[\large Vertex = \frac{ -2 }{ 2(1) }\]

\[\large Vertex = \frac{ -2 }{ 2 }\]

\[\large Vertex = -1 \]

This is your 'x' coordinate of your vertex....already we can tell your answer choice is...?

Answer 6

so the answer is B
minimum (-1,-9)

Answer 7

That would be correct! And just for future reference...if you NEEDED to find the y-value of the vertex....you would simply plug in the x-value into your equation and solve for 'y'

Answer 8

oh I knew about the plugin on how to find the y, so thank you for the help your a life savior.

Answer 9

No problem! :)