Perhatikan gambar ! Besar x + y + z

80 dan 2y membentuk garis lurus
80 + 2y = 180
2y = 180 - 80
2y = 100
y = 100/2 = 50 derajat.

2y --> 2(50) = 100 derajat

40 , 2y , dan 4z membentuk segitiga (total 180)
40 + 2y + 4z = 180
40 + 100 + 4z = 180
4z = 180 -100 - 40
4z = 40
Z = 40/4 = 10

40 dan 7x membentuk garis lurus
40 + 7x = 180
7x = 180 - 40 = 140
x = 140/7 = 20

Simpulan :
X = 20
y = 50
z = 10

20 + 50 + 10 = 80

40° + 7x = 180°
7x = 140°
x = 20°

2y + 80° = 180°
2y = 100°
y = 50°

4z = 180° - 2y - 40°
4z = 180° - 2 × 50° - 40°
4z = 180° - 100° - 40°
4z = 40°
z = 10°

x + y + z
= 20° + 50° + 10°
= 80°