You can put this solution on YOUR website! f(x)=-12x^2+84x
Find the vertex
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To find the vertex, you must see the equation in standard form: y=A(x-h)^2+k, with (h,k) being the (x,y) coordinates of the vertex.
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y=-12x^2+84
This equation of a parabola is in standard form with h=0, k=84 and A=-12
The negative sign of the lead coefficient means the parabola opens downwards and has a maximum=84.
Coordinates of the vertex are (0, 84)