Question

(x2 - 5x + 2) + (x2 + 4x + 5) - (x2 - 6x - 42)

Answer 1

Distribute the negative through the 3rd brackets

(x^2 -5x +2) + (x^2 + 4x +5) -x^2 + 6x + 42 =
x^2 -5x +2 + x^2 +4x + 5 - x^2 + 6x + 42 =

Combine like terms

x^2 + 5x + 49

Won't factor, so... done.