|
(1)AB = OB-OA= (1,1)AD = OD-OA = (-3,3)AB.AD =(1,1).(-3,3) = 0=> AB垂直AD(2)let C(x',y')AB = DC(1,1) = (3-x',2-y')x' = 2 and y' = 1C(2,1)(3)let M(x,y)OM = kOD(x,y) = (-k,4k)S= MA.MB = (OA-OM).(OB-OM) =(2+k, 1-4k).(3+k, 2-4k) =(2+k)(3+k)+ (1-4k)(2-4k) = 6 + 5k+k^2 +2-12k+16k^2 =17k^... |
