When a concentric circle of radius r is transferred into triangle with base r, and height 2πr, then the area of the triangle=?

$$\begin{gathered} \begin{array}{c}When a concentric circle of radius is transferred into triangle \\ \\ with base r, and height 2\pi r,\\ Then the area of the triangle \\ \\ =\frac{1}{2}\times \pi \times 2\pi r=\pi r^2\\ Circles that have the same center \\ but different radius are called Concentric circles.\end{array} \end{gathered}$$