A=5x的平方+4x减1=5x²+4x-1,
B=负x的平方减3x+3=-x²-3x+3,
C=8减7x减6x的平方=8-7x-6x²,
A-B+C
=(5x²+4x-1)-(-x²-3x+3)+(8-7x-6x²)
=5x²+4x-1+x²+3x-3+8-7x-6x²
=5x²+x²-6x²+4x+3x-7x-1-3+8
=4
与x的取值无关.
A=5x的平方+4x减1=5x²+4x-1,
B=负x的平方减3x+3=-x²-3x+3,
C=8减7x减6x的平方=8-7x-6x²,
A-B+C
=(5x²+4x-1)-(-x²-3x+3)+(8-7x-6x²)
=5x²+4x-1+x²+3x-3+8-7x-6x²
=5x²+x²-6x²+4x+3x-7x-1-3+8
=4
与x的取值无关.