関連ワード:  what is area of a circle class 9    what is circumference of a circle class 9    what is radius of a circle class 9    what is sector of a circle class 9    what is segment of a circle class 9    what is chord of a circle class 9    what is tangent of a circle class 9    what is arc of a circle class 9    what is secant of a circle class 9    what is the formula of area of circle class 9