Ada yang tahu cara penyelesaiannya nggak? Masih bingung, nih.

BD : DC = 1 : 2
=> BD = 1/3 BC
=> DC = 2/3 BC

AE : EC = 3 : 1
=> AE = 3/4 AC
=> EC = 1/4 AC

ED = EC + CD
= 1/4 AC + 2/3 CB
= 3/12 AC + 8/12 CB
= (3 AC + 8 CB)/12
= (3(c - a) + 8 (b - c)) / 12
= (3c - 3a + 8b - 8c) / 12
= (-3a + 8b - 5c) / 12
= 1/12 (-3a + 8b - 5c)