Thread: proving

how can i do
(a+b+c)(1/a + 1/b + 1/c)>= 9

is there any theorem to use?
i dont know theorems based on this..
can u help me with this?

Originally Posted by nh149

how can i do
(a+b+c)(1/a + 1/b + 1/c)>= 9

is there any theorem to use?
i dont know theorems based on this..
can u help me with this?

Without conditions on a, b and c this question makes no sense

actually, we must just precise that a, b , c are three positif reals not null.

indeed, we can apply the Cauchy-Schwarz's inegalitie:

we have directly:



cqfd

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