Đáp án:
A= (2x+3y)+(5x+11y)= 2x+3y+5x+11y= 7x+14y
B= (x+y+2z)+(3x-8y)= x+y+2z+3x-8y= 4x-7y+2z
C= (5x-y+z)+(-x+3z-2y)= 5x-y+z-x+3z-2y= 4x-3y+4z
D= (6x-y+z)-(x+z-3y)= 6x-y+z-x-z+3y= 5x+2y
E= (z-x-y)-(-y+z-x)= z-x-y+y-z+x= 0
F= (x²-2x+6)+(5-4x-x²)= x²-2x+6+5-4x-x²= -6x+11
G= (-1+3x-8x²)+(-6x+x²+9)= -1+3x-8x²-6x+x²+9= -7x²-3x+8
H= (7x²+2-5x)-(x²-5x+2)= 7x²+2-5x-x²+5x-2= 6x²
I= (3x²+6x-9)-(3x²+5x-10)= 3x²+6x-9-3x²-5x+10= x+1
K= (x²-8x-11)-(2x²-7x-11) = x²-8x-11-2x²+7x+11= -x²-x