若x-y=5,xy=6,则x+y=

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若x-y=5,xy=6,则x+y=
若x-y=5,xy=6,则x+y=

若x-y=5,xy=6,则x+y=
(x-y)²+4xy=(x+y)²=5²+4×6=49 x+y=±7

x+y)^2=(x- y)^2+4xy
=25+24
=49

x+y=7或－7

若x-y=5,xy=6 ，
那么：（x+y)^2=(x- y)^2+4xy
=25+24
=49
则： x+y=土7 。

x=5+y, xy=(5+y)y=5y+y^2=6, (y-1)(y+6)=0, y1=1,y2=-6

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