a)P=4\(x^3\) - 7\(x^2\) + 3\(x\) - 12
=(4\(x^3\)-7\(x^2\))+(3\(x\))+(-12)
=-3\(x^3\)+3\(x\)-12
Q=-2\(x^3\) + 2\(x^2\) + 12 + 5\(x^2\) - 9
=(-2\(x^3\))+(2\(x^2\)+5\(x^2\))+(12-9)
=-2\(x^3\)+7\(x^2\)+3
b)
P+Q=(-3\(x^3\)+3x-12)+(-2\(x^3\)+7\(x^2\)+3)
=(-3\(x^3\)-2\(x^3\))+(7\(x^2\))+(3x)+(-12+3)
=-5\(x^3\)+7\(x^2\)+3x-9