SOLUTION: y=-3x^2-9x-12 need help finding the vertex and axis

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Question 709270: y=-3x^2-9x-12 need help finding the vertex and axis
Answer by josgarithmetic(39838) About Me  (Show Source):
You can put this solution on YOUR website!
EDIT: Fixed the sign mistake.

First, factor. Then complete the square.
y=-3%28x%5E2%2B3x%2B4%29
The square to add and subtract is %283%2F2%29%5E2.
y=-3%28x%5E2%2B3x%2B%283%2F2%29%5E2+%2B4-%283%2F2%29%5E2%29
y=-3%28%28x%2B%283%2F2%29%29%5E2%2B%287%2F4%29%29
y=-3%28x%2B3%2F2%29%5E2%2B7%2F4
y=-3%28x%2B3%2F2%29%5E2-21%2F4
y=-3%28x%2B3%2F2%29%5E2-5%261%2F4%29


The value of "h" is -%283%2F2%29 and the value of "k" is -%2821%2F4%29 or -%285%261%2F4%29.
The vertex is (-%283%2F2%29,-5%261%2F4)