ntar ku kasih terbrainly, materi Vektor kelas X, thanks

OABCDE segi enam beraturan, maka
OA = AB = BC = CD = DE = EA = a

adb :
a + b + c + d + e = 3(d + a)

bukti :
a + b + c + d + e = 3(d + a)
a + (a + AB) + (a + AB + BC) + (a + AB + BC + CD) + (a + AB + BC + CD + DE) = 3(a + AB + BC + CD + a)
a + 2a + 3a + 4a + 5a = 3(a + 3a + a)
15a = 3(5a)
15a = 15a (terbukti)