Joel is thinking of a quadratic and Eve is thinking of a quadratic. Both use x as their variable. When they evaluate their quadratics for x=1
they get the same number. When they evaluate their quadratics for x=2
they both again get the same number. And when they evaluate their quadratics for x=3
they again both have the same result. Are their quadratics necessarily the same?
If x=1 results in k1
x=2
in k2
and x=3
in k3
then three equations can be made by inputting these values in ax2+bx+c=ki a+b+c=k1 4a+2b+c=k2 9a+3b+c=k3
Using these equations we find the quadratic coefficients in terms of ki
:a=k1−2k2+k32 b=−5k1+8k2−3k32 c=3k1−3k2+k3