(1)1/X-1/Y=3
(Y-X)/XY=3
Y-X=3XY,X-Y=-3XY
(2X-3XY-2Y)/(X-2XY-Y)
=[2(X-Y)-3XY]/(X-Y-2XY)
=(-6XY-3XY)/(-3XY-2XY)
=(-9XY)/(-5XY)
=9/5
(2)X²+3X+1=0
X²+1=-3X
由于X不等于0,两边同时除以X:X+1/X=-3
X²+1/X²
=(X+1/X)²-2X×1/X
=(-3)²-2
=7
(1)1/X-1/Y=3
(Y-X)/XY=3
Y-X=3XY,X-Y=-3XY
(2X-3XY-2Y)/(X-2XY-Y)
=[2(X-Y)-3XY]/(X-Y-2XY)
=(-6XY-3XY)/(-3XY-2XY)
=(-9XY)/(-5XY)
=9/5
(2)X²+3X+1=0
X²+1=-3X
由于X不等于0,两边同时除以X:X+1/X=-3
X²+1/X²
=(X+1/X)²-2X×1/X
=(-3)²-2
=7