B A+B+C 2 A 2 +B2+C 2 A+B+c 2 r. Pr jPPo=pp n 0 B(y0-y1) C(z0-z1) √A2+B2+C2A2+B2+C2、A2+B2+C2 王=4n+n十20-(4十,+,), 42+B2+C 上页      + + + + + + = 2 2 2 2 2 2 2 2 2 0 , , A B C C A B C B A B C A n 0  Pr j n P1P0 = P1P0  n 2 2 2 0 1 2 2 2 0 1 2 2 2 0 1 ( ) ( ) ( ) A B C C z z A B C B y y A B C A x x + + − + + + − + + + − = , ( ) 2 2 2 0 0 0 1 1 1 A B C Ax By Cz Ax By Cz + + + + − + + =