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OABC is a parallelogram with (→OA)=a and (→OC)=c.E is the mid-point of OA.D is a point on BC such that CD:DB=2:1 and F is a point on ED such that EF:FD=3:1.Express the following vectors in terms of a and c (a)(→OD) and (→OE) (b)(→OF)

最佳解答:

a) →OD =→OC+→CD =→OC+2/3→CB =→OC+2/3→OA =→c+2/3→a →OE =1/2→a b) →ED =→EO+→OD = -1/2→a+→c+2/3→a =1/6→a+→c →EF =3/4→ED =1/8→a+3/4→c →OF =→OE+→EF =1/2→a+1/8→a+3/4→c =9/8→a+3/4→c 希望可以幫到你啦

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