已知x²-2x=5,
x²=2x+5
代数式x的四次方+3x³-12x²-31x-15
=(2x+5)²+3x(2x+5)-12(2x+5)-31x-15
=4x²+20x+25+6x²+15x-24x-60-31x-15
=10x²-20x-50
=10(x²-2x)-50
=10*5-50
=0
已知x²-2x=5,
x²=2x+5
代数式x的四次方+3x³-12x²-31x-15
=(2x+5)²+3x(2x+5)-12(2x+5)-31x-15
=4x²+20x+25+6x²+15x-24x-60-31x-15
=10x²-20x-50
=10(x²-2x)-50
=10*5-50
=0