[Lí 8] Vận tốc trung bình

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sangbaby_one

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pinkylun

sv1+sv2=2svtb\dfrac{s}{v_1} + \dfrac{s}{v_2} = \dfrac{2s}{ v_{tb} }

=>s(1v1+1v2)=2svtb=>s(\dfrac{1}{v_1}+\dfrac{1}{v_2})=\dfrac{2s}{v_{tb}}

=>1v1+1v2=2vtb=>\dfrac{1}{v_1}+\dfrac{1}{v_2}=\dfrac{2}{v_{tb}}

=>1v2=2vtb−1v1=2v1−vtbvtb.v1=>\dfrac{1}{v_2}=\dfrac{2}{v_{tb}}-\dfrac{1}{v_1}=\dfrac{2v_1-v_{tb}}{v_{tb}.v_1}

=>v2=vtb.v12v1−vtb=>v_2=\dfrac{v_{tb}.v_1}{2v_1-v_{tb}} đpcm
 
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