679:PS:squares在xy-plane里,且s的面积为1,问下面哪两点坐标在square的边上? A.(1/2,1/2)(3/4,3/2) B.(1/2,0)(0,2) C.(0,1)(3,1) 是列出直线的式子往里带么? ====================================================== 760:有一题好像没见过,是说有一个CUBE, 有EDGE命名为 P1,中点是 E1,还有一个 EDGE E2 中点是P2,然后问求P1P2的长度 (1)CUBE边长是 5 (2)E1和E2不在一个平面内 ============================================================================================== Ps: Wong paid 6 dollars more than Ben but 15% less than H, what is thetotal amount of bill paid by three of them if H paid $24 答案是 18+12+24=54 18是怎么算出来的?.......