Question 297681
In which direction does the parabola for the quadratic equation 
y = -x^2 + 12x + 15 open?
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Do you see that as x gets larger and larger the -x^2 term
has the greatest effect on the value of "y"?
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So, as x gets approaches +inf, -x^2 gets more and more negative.
And, as gets approaches -inf, -x^2 gets more and more negative.
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Since both tails of the parabola get more and more negative,
the parabola opens downward.
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Cheers,
Stan H.