stii ca masura unghiurilor unui triunghi este egala cu 180 grade.adica :
mA+mB+mC=180grade
a)mA+mB+mC=180
54+49+mC=180,de aici,mC=180-103=77grade
b)mA+mB+mC=180
45+90+mC=180,de aici,mC=180-135=45grade
c)mA+mB+mC=180
55°38'49"+ mB+38°45'39"=180,de aici,mB=180-94°24'28"=85°35'32"