[Lí 8] Vận tốc trung bình

P

pinkylun

$\dfrac{s}{v_1} + \dfrac{s}{v_2} = \dfrac{2s}{ v_{tb} }$

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

$=>\dfrac{1}{v_1}+\dfrac{1}{v_2}=\dfrac{2}{v_{tb}}$

$=>\dfrac{1}{v_2}=\dfrac{2}{v_{tb}}-\dfrac{1}{v_1}=\dfrac{2v_1-v_{tb}}{v_{tb}.v_1}$

$=>v_2=\dfrac{v_{tb}.v_1}{2v_1-v_{tb}}$ đpcm
 
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