`a)` Vẽ hình bình hành `ABIO`
Ta có:
`AC = BD = sqrt{a^2 + a^2} = asqrt{2}`
`=> AO = BO = (a\sqrt{2})/2`
Gọi `AI ∩ BO = M`
`=> OM = 1/(2)OB = (a\sqrt{2})/4`
`|vec{DC} - vec{OA}|`
`= |vec{AB} + vec{AO}|`
`= |vec{AB} + vec{BI}|`
`= |vec{AI}|`
`= AI`
`= 2.sqrt{((a\sqrt{2})/2)^2 + ((a\sqrt{2})/4)^2}`
`= (a\sqrt{10})/2`
`b) |vec{AB} + vec{AD} + vec{CB}|`
`= |vec{AC} + vec{CB}|`
`= |vec{AB}|`
`= AB`
`= a`
`c) |vec{AO} + vec{AB} + vec{OD}|`
`= |vec{AD} + vec{AB}|`
`= |vec{AC}|`
`= asqrt{2}`
`d)` Vẽ hình thang cân `ABIN`
`=> AI = BN = (a\sqrt{10})/2`
`|vec{AO} + vec{CD} + vec{BA}|`
`= |vec{AO} + 2vec{BA}|`
`= |vec{BO} + vec{BA}|`
`= |vec{BN}|`
`= BN`
`= (a\sqrt{10})/2`
