That is, CD (vector) =λ(CD-AD) (vector) +μ(CD+DB) (vector),

CD (vector) =λCD (vector) +μCD (vector) -λAD+μDB, (and AD (vector) = =2DB (vector))

So CD (vector) = (λ+μ) CD (vector)-2λ db+μ db,

CD (vector) =(λ+μ)CD (vector)

+(μ-2λ)DB，

So λ+μ= 1, μ-2λ=0.

λ= 1/3,μ=2/3,

λμ=2/9, choose A.