PLEASE HELP! Test tomorrow - dont understand?

  • Thread starter Thread starter Ellen An
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Ellen An

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Y=ax^2+bx+c goes through points (-1,22), (1,8), (3,10), (-2,p) (q,17) -> what are p and q?
 
Use the first 3 points to set up 3 equations in 3 unknowns (a,b,c):

22 = a - b + c
8 = a + b + c
10 = 9a + 3b + c

Solve that for a, b, and c using the usual tricks: add the first two equations to get

30 = 2a + 2c, or a = 15 - c

Subtract the first two equations to get 14 = -2b, or b = -7.

Plug both of those into the first equation to get 22 = 9(15-c) - 3(-7) + c, after which you find c = 13. Then a = 2. Using those values, plug in the other two points, with missing x or y, and solve for what the p or q value must be to make the equation correct, now that you know what the coefficients a, b, and c are.

y=2x^2 - 7x + 13.

For the first unknown point, x = -2, so y = 2*(-2)^2-7(-2)+13 = 35.

For the second unknown point, you get

17 = 2q^2 -7q + 13. Using the quadratic equation,

q = {7 +/- sqrt(49-104)}/2*2. Unless you have a typo in the question, there is no real value q that satisfies the equation. There are two complex numbers that do, but I suspect you are not at the level of math yet where you are dealing with complex numbers. If you are, you know what to do from here.
 
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