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December 22, 2014

December 22, 2014

Posted by **tommas** on Sunday, October 17, 2010 at 6:56am.

y=x^2-5x-8 at the points A and B.

the curve y=p+qx-2x^2 also passes through ponts A and B. what are the values of p and q??

helpppppplease...thanks

- math -
**Reiny**, Sunday, October 17, 2010 at 8:05amFirst, find the intersection of y = x-1 with y = x^2 - 5x - 8

that is, solve

x^2 - 5x - 8 = x - 1

x^2 - 6x - 7 = 0

(x-7)(x+1) = 0

x = -7 or x = -1

sub that back into y = x-1 to get

y = 6 or y = -2 respectively

so we have A(7,6) and B(-1,-2)

since these two points also lie on ty = p + qx - 2x^2 let's sub them in

6 = p + 6q - 98 and

-2 = p -q - 8

re-arrange these two equations and solve.

They are easy to solve as it by subtracting them, since the p's are the same.

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