Question

(2x^4 - 6x^2+8) + (-x^4+ 2x^2-12)

Answer 1

(2x^4 - 6x^2+8) + (-x^4+ 2x^2-12)
=2x^4-6x^2-x^4+2x^2-12
=x^4-4x^2-12

Just watch your signs when opening up the brackets and then collect like terms.