Bài bồi dưỡng Lý 8

C

cbtruong

L

lp_qt

$v_{tb}=\frac{S}{t}$

$=\dfrac{S}{\dfrac{\dfrac{S}{2}}{v_{1}}+\dfrac{ \dfrac{S}{2}}{v_{2}}}$

$=\dfrac{2.v_{1}.v_{2}}{v_{1}+v_{2}}$

*cm

$\dfrac{v_{1}+v_{2}}{2}$ \geq $\dfrac{2.v_{1}.v_{2}}{v_{1}+v_{2}}$

$\Longleftrightarrow (v_{1}+v_{2})^{2}$ \geq $4.v_{1}.v_{2}$

$\Longleftrightarrow (v_{1}-v_{2})^{2}$ \geq $0$ (luôn đúng )
 
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