Suppose the radius of a circle is \color{R_COLOR}{R}. What is its diameter?
We know d = 2r, so d = 2 \cdot \color{R_COLOR}{R} = \color{D_COLOR}{2 * R}.
Suppose the diameter of a circle is \color{D_COLOR}{2 * R}. What is its radius?
We know d = 2r, so r = d / 2 and r = \color{D_COLOR}{2 * R} / 2 = \color{R_COLOR}{R}.
Suppose the radius of a circle is \color{R_COLOR}{R}. What is its circumference?
We know c = 2\pi r, so c = 2 \pi \cdot \color{R_COLOR}{R} = \color{C_COLOR}{2 * R\pi}.
Suppose the circumference of a circle is \color{C_COLOR}{2 * R\pi}. What is its radius?
We know c = 2\pi r, so r = c / 2\pi = \color{C_COLOR}{2 * R\pi} / 2 \pi = \color{R_COLOR}{R}.
Suppose the diameter of a circle is \color{D_COLOR}{2 * R}. What is its circumference?
We know c = \pi d, so c = \pi \cdot \color{D_COLOR}{2 * R} = \color{C_COLOR}{2 * R\pi}.
Suppose the circumference of a circle is \color{C_COLOR}{2 * R\pi}. What is its diameter?
We know c = \pi d, so d = c / \pi = \color{C_COLOR}{2 * R\pi} / \pi = \color{D_COLOR}{2 * R}.