问题标题：
(1)若x-1/x=3,则x^2+1/x^2=_____________(2)已知x/2=y/3=z/4,则2x+y-z/3x-2y+z=____________(3)计算,(1/a-1)-1-a
问题描述：
(1)若x-1/x=3,则x^2+1/x^2=_____________
(2)已知x/2=y/3=z/4,则2x+y-z/3x-2y+z=____________
(3)计算,
(1/a-1)-1-a
黄建成回答：
1)若x-1/x=3,则x^2+1/x^2=_____________平方x^2-2*x*1/x+1/x^2=3^2=9x^2+1/x^2=9+2=11(2)已知x/2=y/3=z/4,则2x+y-z/3x-2y+z=____________x/2=y/3=z/4=kx=2k,y=3k,z=4k(2x+y-z)/(3x-2y+z)=(4k+3k-4k)/(6k-6k+4k)=3k...
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