randRange(1, 8)

Suppose the radius of a circle is `\color{R_COLOR}{R}`. What is its area?

Math.PI * R * R
initCircle( R ); drawRadius( R );

We know `K = \pi r^2`, so `K = \pi \cdot \color{R_COLOR}{R}^2 = \color{K_COLOR}{R * R\pi}`.

drawArea( R );
randRange(1, 8)

Suppose the area of a circle is `\color{K_COLOR}{\pi}`. What is its radius?

Suppose the area of a circle is `\color{K_COLOR}{R * R\pi}`. What is its radius?

R
initCircle( R ); drawArea( R );

We know `K = \pi r^2`, so `r = \sqrt{K / \pi} = \sqrt{\color{K_COLOR}{R * R\pi} / \pi} = \color{R_COLOR}{R}`.

drawRadius( R );
randRange(1, 8)

Suppose the diameter of a circle is `\color{D_COLOR}{2 * R}`. What is its area?

Math.PI * R * R
initCircle( R ); drawDiameter( R );

First, find the radius: `r = d/2 = \color{D_COLOR}{2 * R}/2 = \color{R_COLOR}{R}`.

Now find the area: `K = \pi r^2`, so `K = \pi \cdot \color{R_COLOR}{R}^2 = \color{K_COLOR}{R * R\pi}`.

drawArea( R );
randRange(1, 8)

Suppose the area of a circle is `\color{K_COLOR}{\pi}`. What is its diameter?

Suppose the area of a circle is `\color{K_COLOR}{R * R\pi}`. What is its diameter?

2 * R
initCircle( R ); drawArea( R );

First, find the radius: `K = \pi r^2`, so `r = \sqrt{K / \pi} = \sqrt{\color{K_COLOR}{R * R\pi} / \pi} = \color{R_COLOR}{R}`.

Now find the diameter: `d = 2r = 2\cdot \color{R_COLOR}{R} = \color{D_COLOR}{2*R}`.

drawDiameter( R );
randRange(1, 8)

Suppose the circumference of a circle is `\color{C_COLOR}{2 * R\pi}`. What is its area?

Math.PI * R * R
initCircle( R ); drawCircumference( R );

First, find the radius: `r = c/2\pi = \color{C_COLOR}{2 * R\pi}/2\pi = \color{R_COLOR}{R}`.

Now find the area: `K = \pi r^2`, so `K = \pi \cdot \color{R_COLOR}{R}^2 = \color{K_COLOR}{R * R\pi}`.

drawArea( R );
randRange(1, 8)

Suppose the area of a circle is `\color{K_COLOR}{\pi}`. What is its circumference?

Suppose the area of a circle is `\color{K_COLOR}{R * R\pi}`. What is its circumference?

Math.PI * 2 * R
initCircle( R ); drawArea( R );

First, find the radius: `K = \pi r^2`, so `r = \sqrt{K / \pi} = \sqrt{\color{K_COLOR}{R * R\pi} / \pi} = \color{R_COLOR}{R}`.

Now find the circumference: `c = 2\pi r = 2\pi \cdot \color{R_COLOR}{R} = \color{C_COLOR}{2*R\pi}`.

drawCircumference( R );