Area of Circle/Proof 3/Lemma 1

Lemma for Area of Circle: Proof 3

 * Area-of-Circle-Proof-3.png

Construct a circle with radius $r$ and circumference $c$, whose area is denoted by $C$.

Construct a triangle with height $r$ and base $c$, whose area is denoted by $T$.

Then:
 * $T = \pi r^2$