已知A(1,2)B(3,-2)C(9,7),若E,F为线段BC的三等份点,则AE向量×AF向量=
人气：341 ℃ 时间：2019-10-17 05:00:32
解答
E,F为线段BC的三等份点=> |BE|:|EC| = 1:2 and |BF|:|FC| = 2:1=> OE = (2OB+OC)/3 and OF = (OB+2OC)/3AE .AF= (OE-OA).(OF-OA)=( (2OB+OC)/3 - OA) .( (OB+2OC)/3 - OA)= ( (5,1) - (1,2) ) .( (7,4) - (1,2))= (4...
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