Find an equation in standard form of the parabola passing through the points (1, -2), (2,-2), (3,-4)

The standard form of a parabola is y=ax²+bx+c
use the three given points to find the three unknown constants a, b, and c:
-2=a+b+c1
-2=4a+2b+c 2
-4=9a+3b+c3
equation 2 minus equation 1: 3a+b=04
equation 3 minus equation 2: 5a+b=-25
equation 5 minus equation 4: 2a=-2, so a=-1
plug a=-1 in equation 4: -3+b=0, so b=3
Plug a=-1, b=3 in equation 1: -2=-1+3+c, so c=-4
the parabola is y=-x²+3x-4

double check: when x=1, y=-1+3-4=-2
when x=2, y=-4+6-4=-2
when x=3, y=-9+9-4=-4
Yes.

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