Area of Triangle

Consider rectangle ABCD

Area ABCD = ABxCD ..... Definition

Draw diagonal AC

∇ABC = ∇ADC ... Diagonal of parallelogram creates equal triangles

∴ Area ∇ABC = 1/2 ABxBC

Redraw ∇ABC and draw ∇APB such that P is on parallel lines AB and DC extended.

Area ∇APC = ∇ABC = 1/2 ABxBC ... Triangles on same base between parallels have equal areas

∴ Area of triangle = 1/2 Base x Height