a)
Ta có: M = 4x²y² - 2xy + x-1
N= -3/2x +2xy - 4x²y² +3
=>M-N= (4x²y² - 2xy + x-1)-(-3/2x +2xy - 4x²y² +3)
= 4x²y² - 2xy + x-1 +3/2x -2xy + 4x²y² -3
= (4x²y²+ 4x²y) + (- 2xy-2xy) +(x +3/2x)+ (-1-3)
=8x²y² - 4xy + 5/2x -4
Vậy M-N= 8x²y² - 4xy +5/2x -4
b)
Ta có: M = 4x²y² - 2xy + x-1
N= -3/2x +2xy - 4x²y² +3
=>M+N= (4x²y² - 2xy + x-1)+(-3/2x +2xy - 4x²y² +3)
= 4x²y² - 2xy + x-1 -3/2x +2xy - 4x²y² +3
= (4x²y² - 4x²y²) + (- 2xy+2xy) + ( x-3/2x) + (-1+3)
= -1/2x+2 (1)
Thay x=1 vào (1)
Ta được:
M+N=(-1/2).1+2
= -1/2+2
= 3/2
Vậy M+N= 3/2 khi x=1
c)
Thay M+N=5 vào (1)
Ta được:
-1/2x+2=5
-1/2x =5-2
-1/2x = 3
x = 3:(-1/2)
x = -3/2
Vậy x=-3/2 khi M+N=5
