x+y=1 xy=-1 求x立方+y立方?求x的4次方+y的4次方?好的话有更高的酬劳哦!

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x+y=1 xy=-1 求x立方+y立方?求x的4次方+y的4次方?好的话有更高的酬劳哦!

x+y=1 xy=-1 求x立方+y立方?求x的4次方+y的4次方?好的话有更高的酬劳哦!
x+y=1 xy=-1 求x立方+y立方?求x的4次方+y的4次方?
好的话有更高的酬劳哦!

x+y=1 xy=-1 求x立方+y立方?求x的4次方+y的4次方?好的话有更高的酬劳哦!
x³+y³
=(x+y)(x²-xy+y²)
=(x+y)[(x+y)²-3xy]
=1×[1²-3×(-1)]
=1×(1+3)
=1×4
=4
x^4+y^4
=(x^4+y^4+2x²y²)-2x²y²
=(x²+y²)²-2x²y²
=[(x+y)²-2xy]²-2x²y²
=[1²-2×(-1)]²-2×(-1)²
=(1+2)²-2×1
=3²-2
=9-2
=7

x的4次方+y的4次方=(x²+y²)²-2(xy)²=(x²+y²)²-2
而x²+y²=(x+y)²-2xy=1+2=3
则:x的4次方+y的4次方=3²-2=7

∵x+y=1 xy=-1
∴x³+y³=(x+y)(x²-xy+y²)=(x+y)[(x+y)²-3xy]=1×(1+3)=4
x的4次方+y的4次方
=(x²)²+(y²)²
=(x²+y²)²-2x²y²
=[(x+y)²-2xy]²-2(xy)²
=[1+2]²-2
=9-2=7