责任书格式怎么写:╃■帮帮忙〓?

来源:百度文库 编辑:查人人中国名人网 时间:2024/03/30 00:04:38
已知1/x-1/y=5,xy=-1,则1/(x^4)+1/(y^4)=________.

因为1/X-1/Y=5
所以(1/X-1/Y)^2=25
即1/(X^2)+1/(Y^2)-2[1/(XY)]=25
因为XY=-1
所以1/(X^2)+1/(Y^2)=27
因为1/(X^2)+1/(Y^2)=27
所以[1/(X^2)+1/(Y^2)]^2=27^2
即1/(X^4)+1/(Y^4)+2[1/(XY)^2]=27^2
因为XY=-1
所以(XY)^2=1
所以1/(X^4)+1/(Y^4)=27^2-2
所以1/(X^4)+1/(Y^4)=727

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