2x²+6xy+9y²-2x+1 【改为+1】
=(x^2+6xy+9y^2)+(x^2-2x+1)
=(x+3y)^2+(x-1)^2
x+3y=0
x-1=0 x=1 y=-1/3
已知xy为实数2x²+6xy+9y²-2x-1=0 x=?y=?
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