 ’ ’C’ ABC NẾU          B C  C) C = C , ˆ ˆ A B A C...

7)  ’ ’C’ ABC nếu

   

B C

  c) C = C , ˆ ˆ A B A C

 

  b) B = B , ˆ ˆ A B

a) A = A , ˆ ˆ A B B C

AB

AB AC

BC

AB BC