MA=MC+CA=1/6CB+2/3CA+CA=1/6CB+5/3CA,MB=MC+CB=1/6CB+2/3CA+CB=7/6CB+2/3CA
MA*MB=7/36CB2(平方)+37/18CA*CB*COS60+10/9CA2=7/3+37/3+40/3=28
MA=MC+CA=1/6CB+2/3CA+CA=1/6CB+5/3CA,MB=MC+CB=1/6CB+2/3CA+CB=7/6CB+2/3CA
MA*MB=7/36CB2(平方)+37/18CA*CB*COS60+10/9CA2=7/3+37/3+40/3=28