Answer with explanation:
Given: In △ABC with side lengths a, b, and c, and height h, a vertical line extends from angle B perpendicular to side b.
To prove:→ Area(ΔABC)

Proof:
In △ABC with side lengths a, b, and c, and height h ,
Area of ΔABC

Let perpendicular from angle , B on the side AC cuts AC at M.
Definition of sine

Area of Triangle ΔABC

-----Using Substitution Property,that is , h=a sin C
→Area = 1/2 b h