A=X^2-10X+5 B=-X^2-5X
A+B=X^2-10X+5 -X^2-5X =-15X+5
A-2B=X^2-10X+5 -2(X^2-5X )=X^2-10X+5 -2X^2+10X =-X^2+5
数学辅导团为您解答