简单计算一下即可，答案如图所示
φ(cx-az, cy-bz) = 0,令 u= cx-az， v = cy-bzφ'u' + φ'v' = 0φ'u' + φ'v' = 0得 φ'(c-az') + φ'(-bz') = 0 φ'(-az') + φ'(c-bz') = 0得 z' = c φ'/[a φ'+b φ']z' = c φ'/[a φ'+b φ']则 az'+bz' = c
