What is the equation in vertex form of a parabola with vertex (2,4) that opens downward and is stretched by a factor of 3?

The "a" in the vertex form is the same "a" as. in y = ax2 + bx + c (that is, both a's have exactly the same value). The sign on "a" tells you whether the quadratic opens up or opens down. Think of it this way: A positive "a" draws a smiley, and a negative "a" draws a frowny.

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