Answer:
(a) 3 must be factored from 3x^2 + 9x
Step-by-step explanation:
The first step when rewriting a quadratic from standard form to vertex form is to factor out the leading coefficient from the variable terms.
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y = 3x^2 +9x -18 . . . . . . given
y = 3(x^2 +3x) -18 . . . . . leading coefficient factored out
y = 3(x^2 +3x +2.25) -18 -3(2.25) . . . . . complete the square
y = 3(x +1.5)^2 -24.75 . . . . . simplify to vertex form
