If s △ abd = 1 / 2S △ ACD, then AB: AC=

If s △ abd = 1 / 2S △ ACD, then AB: AC=

Through point D, make de perpendicular to AB and E, DF perpendicular to AC and F
Then de = DF
Because s △ abd = 1 / 2S △ ACD
So 1 / 2Ab * de = 1 / 2 * 1 / 2Ac * DF
So 2Ab = AC
AB:AC=1:2