I am not understanding your question. This is what the problem is (-7y^2-4y+6)=(7y^2-4y-4)-(2y^2-2y-6)Simplifying a sum or difference of three univariate polynomials

Question

I am not understanding your question. This is what the problem is (-7y^2-4y+6)=(7y^2-4y-4)-(2y^2-2y-6)Simplifying a sum or difference of three univariate polynomials

Answer 1

-7y^2-4y+6 = 7y^2-4y-4-2y^2+2y+6.

-12y^2-2y+4 = 0.
Divide by -2:
6y^2 + y - 2 = 0.
A*C = -12 = 4*(-3)
6y^2 + (4y-3y) - 2 = 0.
(6y^2+4y) - (3y+2) = 0.
2y(3y+2) - (3y+2) = 0.
(3y+2)(2y-1) = 0.

3y+2 = 0, Y = -2/3.

2y-1 = 0, Y = 1/2.