Do a two column proof!
given: ab = dc
prove: ac = db
!

AC       =        DB     (Proved)

Step-by-step explanation:

Here, in the triangle ADE

AB = DC (Given)

Now, by EUCLID's LEMMA

If equals are added  to equals, the sum  are equal.

⇒   AB   +   BC   =   DC   +   BC

or,         AC       =        DB    

                 Hence Proved!

step-by-step explanation:

∆abc has the points a(1, 7), b(-2, 2), and c(4, 2) as its vertices. formed with the point d(1, 2) as its third vertex, then ∆abd is triangle.

there is no question content here, but you for the free points! : d