作业帮1.X+Y=5,X-Y=－2,则X²+Y²的值是多少?
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1.X+Y=5,X-Y=－2,则X²+Y²的值是多少?
1.X+Y=5,X-Y=－2,则X²+Y²的值是多少?
1.X+Y=5,X-Y=－2,则X²+Y²的值是多少?
X²+Y²=(X+Y)²-2XY=25-2XY (1)
X²+Y²=(X-Y)²+2XY=4+2XY (2)
(1)+(2)
2(X²+Y²)=25+4
X²+Y²=14.5
58/4
14.5
直接解方程组
求解得x=3/2 y=7/2
X2+Y2
=9/4+49/
=58/4
=29/2
=14.5
根据前面两式子，相加可得2X=3，则X=1.5，Y=3.5，则X²+Y²=1.5²+3.5²=2.25+12.25=14.5
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1.X+Y=5,X-Y=－2,则X²+Y²的值是多少?
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