Thread: Simplify and verify.

Hey guys,

the task: Simplify and verify.

(-x^2 + x) (7x^2 + 3x -9)
my calculation:
= -7x^4-3x^3+9x^2+7x^3+3x^2-9x
= -7x^4+4x^3+12x^2-9x

Verification: x = 1

-7x^4+4x^3+12x^2-9x
= -7(1)^4+4(1)^3+12(1)^2-9(1)
= -7+4+12-9
= 0

(-x^2 + x) (7x^2 + 3x -9)
= (-1^2+1) (7(1)^2+3(1)-9)
= (1+1) (7+3-9)
= (2) (1)
= 2

Something is wrong in my verification calculations, because both solutions should agree. Could somebody please explain my mistake?

Originally Posted by ford2008

(-x^2 + x) (7x^2 + 3x -9)
= (-1^2+1) (7(1)^2+3(1)-9)
= (1+1) (7+3-9)

Lines 3. -1 + 1 = 0, not 2.

-Dan