2道数学题
x^2+x-1=0
求x^2+1/x^2和x^3+2x^2+3
x^2-4xy+5y^2-6y+9=0,求(-x-y)^2-(-y+x)(x+y)-2xy
①解:由题意可得x+1-1/x=0
x-1/x=-1
(x-1/x)²=1
x²-2+1/x²=1
x²+1/x²=3
由题意可得x²=1-x,x²+x=1
x³+2x²+3
=x²(x+2)+3
=(1-x)(x+2)+3
=-(x²+x)+2+3
=-1+5
=4
好难呀。。。。你洗洗睡吧
x²+x-1=0
(x+0.5)²-1.25=0
x+0.5=±0.5√5
x=0.5(√5-1)或x=-0.5(√5+1)
1.条件是个一元二次方程,可以解出x;
2.条件原式可变为:(x-2y)^2+(y-3)^2=0可求出x和y
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