1) (x-1)(2x-1)-(x+1)2+1
=2x2-3x+1-x2-2x-1+1
=x2-5x+1
=14+1
=15
2)C=2(2a+S/2a)=2(2a+2a-3b+1)=8a-6b+2
3)（x+y)2=x2+2xy+y2=25,(x-y)2=x2-2xy+y2=9
（x+y)2-(x-y)2=4xy=16
xy=4
（x+y)2+(x-y)2=2x2+2y2=34
x2+y2=17
4)a2+2b2+c2-2ab-2bc
=a2-2ab+b2+c2-2bc+b2
=(a-b)2+(c-b)2=0
(a-b)2=0 (c-b)2=0
a=b c=b
a=b=c
三角形为等边三角形