Question

AD:DC =?

Answer 1

use trigonometry @ganeshie8

Answer 2

@mathmath333

Answer 3

Start with a right triangle, with right angle at B.

Answer 4

Now drop an altitude from the vertex of the right angle to the hypotenuse.

Answer 5

Now you have 3 right triangles, ABC, ABD, and BCD.
Ok so far?

Answer 6

The 3 triangles are similar. This can be shown easily.
Since the 3 triangles are similar, the lengths of corresponding sides are in proportion.

Answer 7

AB : BC : AC = AD :BD : AB = BD : CD : BC