a-b

.(3):

a2=b2+c2-2bccosA b2=c2+a2-2cacosB c2=a2+b2-2abcosC11.

2.:( r)

3. ,.

4.

300

1

AB2=c2=a2+b2-2abcosC

A4ABCasinA=bsinBABC___ (A) (B) (C) (D)acosA=bcosBABC___acosB=bcosAABC___AC

1.2010a,b,cABCA,B,C ,a=1,b= , A+C=2B,sinA=_________________. :

2.2010ABC30,A,B,C

a,b,c, cosA= .

(1) ; (2)cb=1,a. : (1) 144 (2) a =5

3 .(2011)ABCABC a,b,c1 A 2 sinC.1

2: ABC 3 .(2011)ABCABC a,b,c1 A 2 sinC.

P51-52