En paralelogramo abcd

Vector AE=vector AD+vector DE=vector BC+(1/2)vector AB

Vector AF=vector AB+vector BF=vector AB+(1/2)vector BC

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Vector AC=vector AB+vector BC=(2/3)[vector BC+(1/2) vector AB+vector AB+(1/2) vector BC]=(2 /3)(vector AE+vector AF)

∴λ=μ=2/3

∴λ+μ=4/3