P1 + R1 = 180o (dalam sepihak)
128o + R1 = 180o
R1 = 180o – 128o
R1 = 52o
R1 = R2 = 52o
R1 + R2 + R3 = 180o (berpelurus)
52o + 52o + R3 = 180o
104o + R3 = 180o
R3 = 76o
P1 + R1 = 180o (dalam sepihak)
128o + R1 = 180o
R1 = 180o – 128o
R1 = 52o
R1 = R2 = 52o
R1 + R2 + R3 = 180o (berpelurus)
52o + 52o + R3 = 180o
104o + R3 = 180o
R3 = 76o
Editor: Annisa Fadilla
Sumber: Kemendikbud