Ta có: AJ→=BI→=−IB→
CS→=−RA→
PC→=−BQ→
=> $\overrightarrow{RJ} +\overrightarrow{IQ}+\overrightarrow{PS}
= (RA→+AJ→)+(IB→+BQ→)(PC→+CS→)
= (RA→+−IB→)+(IB→+−PC→)+(PC→+−RA→)
= (IB→+−IB→)+(PC→+−PC→)+(RA→+−RA→)=0→ ( đpcm )