Besar sudut BCA adalah

BCA = 180 - (3x-30)
BCA = 210 - 3x

ABC = 180 - (x+40)
ABC = 140 - x

Jumlah Sudut Segitiga ABC = 180°
70 + 210 - 3x + 140 - x = 180
420 - 4x = 180
4x = 180
X = 60

BCA = 180 - (3x-30)
BCA = 180 - (180-30)
BCA = 180- 150
BCA = 30°

Jawab :

ABC + ACB + BAC = 180°
180° - (x + 40) + 180° - (3x - 30) + 70 = 180
240° = 4x
x = 60°

sudut BCA = 180 - (3x - 30) = 30°