一、有关圆内共端点诸弦的长度问题解这类问题一般取以公共端点为极点、圆的直径或切线为极轴建立极坐标系,则弦的另一端点所对应的极径可视为圆内的弦的长度。例1.如图,OP 是⊙O的半径以 OP 为直径的⊙O′与⊙O 的弦 PB 交于C.求证;C 是 PB 的中点证明以 P 为极点,过 P 的切线所在射线为极轴,建立极坐标系。设⊙O 的半径为 R,则⊙O 的方程为p=2Rsinθ.⊙O′的方程为ρ=Rsinθ,∠BPx=α.令θ=α,则 PB=2Rsinα,PC First, the length of the common end of the chords in the circle of the solution to this problem is generally taken to the common endpoint is the pole, the diameter of the circle or tangent for the polar axis to establish a polar coordinate system, the other end of the string corresponding to the polar path visible The length of the chord inside the circle. Example 1. As shown in the figure, OP is the radius of ⊙O with OP of diameter ⊙O′ and ⊙O of string PB in C. Proof; C is the midpoint of PB proves that P is the pole, the tangent of P For the polar axis, establish a polar coordinate system. Let ⊙O be a radius R, then ⊙O equation is p=2Rsinθ. ⊙O′ is ρ=Rsinθ, ∠BPx=α. Let θ=α, then PB=2Rsinα,PC