1..已知(x-y)^2=8,xy=2,求x^4+y^4!2.已知x+1/x=4,求(x-1/x)^2
还是第2题的题目,x^2+1/(x^2)等于多少?大哥哥大姐姐求求你们帮帮忙~
人气:209 ℃ 时间:2020-04-15 03:16:19
解答
1.
x^4+y^4=x^4-2(xy)²+y^4+2(xy)²
=(x²-y²)²+2(xy)²
=(x-y)²(x+y)²+2(xy)²
=(x-y)²[(x-y)²+4xy]+2(xy)²
=8*[8+4*2]+2*4
=136
2.(x-1/x)²
=(x+1/x)²-4=4*4-4=12还是第2题的题目,x^2+1/(x^2)等于多少?
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