若x²+xy-2y²=0则 x²+3xy+y²/x²+y²=()
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若x²+xy-2y²=0则 x²+3xy+y²/x²+y²=()
若x²+xy-2y²=0则 x²+3xy+y²/x²+y²=()
若x²+xy-2y²=0则 x²+3xy+y²/x²+y²=()
填:5/2或-1/5
x²+xy-2y²=0
(x+2y)(x-y)=0
x+2y=0或x-y=0
x=-2y或x=y
于是
x=y时:
(x²+3xy+y²)/(x²+y²)
=(y²+3y²+y²)/(y²+y²)
=5y²/2y²
=5/2
x=-2y时:
(x²+3xy+y²)/(x²+y²)
=(4y²-6y²+y²)/(4y²+y²)
=-y²/5y²
=-1/5