已知x=2-3,y=2+3,求下列代数式的值: (1)x2+2xy+y2; (2)x2-y2.

问题描述:

已知x=2-

3
,y=2+
3
,求下列代数式的值:
(1)x2+2xy+y2;                        
(2)x2-y2

(1)∵x=2-

3
,y=2+
3

∴x+y=4,
∴x2+2xy+y2=(x+y)2=42=16;
(2))∵x=2-
3
,y=2+
3

∴x+y=4,x-y=-2
3

∴x2-y2=(x+y)(x-y)
=4×(-2
3

=-8
3