第1个回答 2011-07-20
解:x^2+y^2
=(x+y)^2-2xy
=3^2-2*1
=9-2=7
(x-y)^2
=(x+y)^2-4xy
=3^2-4*1
=9-4
=5
第2个回答 2011-07-20
(1)x2 + y2
=(x+y)^2-3xy
=9-2
=7
(2) (x-y)2
=(x+y)^2-4xy
=9-4
=5
第3个回答 2011-07-20
x^2 + y^2
=(x+y)^2-2xy
=9-2
=7
(x-y)^2
=x^2+y^2-2xy
=7-2
=5
第4个回答 2011-07-20
第一个为7
第二个为5