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How to solve for a quadratic equation when given three points?

For my math portfolio, I have been given the problem to algebraically solve the equation when given (-2,51), (1,-9), and (5-33).I plugged them into y=a(x)^2+b(x)+c. From there I got the equations;

51=4a-2b+c

-9=a+b+c

-33=25a+5b+c

If I eliminate -9=a+b+c then I get 60=3a-b and -24=24a+4b, but once I solve for a and b I get -22=a and -126=b. This is very off, and I don't know how to solve this. Could someone help me?

Update:

How do I eliminate it properly?

1 Answer

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  • ?
    Lv 7
    7 years ago
    Favorite Answer

    Your method is correct. You have your three equations right

    51=4a-2b+c

    -9=a+b+c

    -33=25a+5b+c

    You just got your elimination wrong, the correct answer is

    a = 2, b = -18, c = 7

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