如果x+y=6,xy=7,那么x²+y²= ,(x-y)²=

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如果x+y=6,xy=7,那么x²+y²= ,(x-y)²=

如果x+y=6,xy=7,那么x²+y²= ,(x-y)²=

x+y=6 xy=7
===> (x+y)²=6²=36
===> x²+y²+2xy=36
===> x²+y²+2*7=36
===> x²+y²=22
(x-y)²=(x+y)²-4xy=6²-4×7=36-28=8

x²+y²
=(x+y)²-2xy
=6²-2*7
=36-14
=22
(x-y)²
=x²+y²-2xy
=22-2*7
=22-14
=8

果x+y=6,xy=7,
那么x²+y²= (x+y)^2-2xy=22
(x-y)²=22-2xy=8

x²+y²=(X+Y)²-2XY =6²-2×7 =36-14 =22
(x-y)²=x²+y²-2XY=22-14=8