Perhatikn gmbr di samping. Besar sudut abc...

Besar sudut ACB...

AC = 180
sudut BEC = 180 - 84 = 96°

jumlah sudut segitiga BEC = 180 = ∠BEC + ∠EBC + ∠ACB
                                              180 = 96 + 52 + ∠ACB
                                          ∠ACB = 180 - (96+52) = 32° (a)