The minimum value of BQ is when the circle is tangent to AC. Because AB=5, BC= 12 and AC= 13, the radius of the circumference = 12-( 13-5) = 4.
The maximum value of BQ is BC, so the range of BQ is 4 ~ 12.
Question 1: Explain the origin of the number "zero"; (1) explained the meaning of "zero" and (1) verified the difficulty of "zero