(1) (5x^2-3)-(2x+5)=5x^2
5x^2 - 3 - 2x - 5 = 5x^2
2x^2 - 10 - 2x = 0
2x^2 - 2x - 10 = 0
x^2 - x - 5 = 0
(x-2)(x+5) = 0
x = 2, x = -5

(2) x^2-(x+1)-(x^2-7x+32)=3
x^2 - x - 1 - x^2 + 7x - 32 = 3
-2x - 33 = 3
-2x = 36
x = -18

(3) (y^3+3y-8)-(5y-y^3+7)=2y^3-2y-15
y^3 + 3y - 8 - 5y + y^3 - 7 = 2y^3 - 2y - 15
2y^3 - 2y - 15 = 2y^3 - 2y - 15
This equation is an identity, therefore, it is true for all real numbers y.