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Consider an acute angled Delta ABC. Let ...

Consider an acute angled `Delta ABC.` Let AD, BE and CF be the altitudes drawn from the vertice to the opposite sides. Prove that : `(EF)/(a)+ (FD)/(b)+ (DE)/©= (R+r)/(R ).`

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`(FE)/(a) + (FD)/(b) + (DE)/(c) = (a cos A)/(a) + (b cos B)/(b) + (c cos C)/(a)`
`= cos A + cos B + cos C`
`le (3)/(2)`
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