如果x平方减2x减1等于0,3x的4次方加5x的3次方减7x平方加5的值

x²-2x-1=0,
x²=2x+1
x=1±√2
3x^4+5x³-7x²+5
=x²(3x²+5x-7)+5
=(2x+1)(6x+3+5x-7)+5
=(2x+1)(11x-4)+5
=22x²+3x+1
=44x+22+3x+1
=47x+23
当x=1+√2时,原式=70+47√2
当x=1-√2时,原式=70-47√2