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19:45
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A: Find the sum : $OP+OQ+OR$ in the triangle below

Math LoverWe have a well known inequality that for any point $O$ interior to a triangle, $OA + OB + OC \gt s$ where $s$ is sub-perimeter. Here, $OA = OB = OC = R$ (circumradius) So, $R \gt \dfrac43$ and hence $R + r \gt \dfrac 43$ As the circumcenter $O$ is inside the triangle, we have an acute triangle a...

For $s \gt 2R + r$, please see Circumradius, Inradius section in en.wikipedia.org/wiki/Acute_and_obtuse_triangles
In the link you given one can find only the next reference and this other reference reads: "1088^⋆.*Proposed by Basil C. Rennie, James Cook University of North Queensland, Australia.* If $R, r, s$ are the circumradius, inradius, and semiperimeter, respectively, of a triangle with largest angle $A$, prove or disprove that $s\, ?\, 2R + r$ according as $A\,?\, 90^\circ$.
@user ok, pls see Section Inradius, exradii, and circumradius in en.wikipedia.org/wiki/List_of_triangle_inequalities and link#35 at the bottom
I see. You probably mean the Lemma 2 from the link#35.
Lemma 2 proves exactly this identity. :)
oh ok, just noticed :)
19:45
I think you should mention this identity in the answer because it is not so well-known.
@MathLover You're back..thank you for the answer
@petaarantes you are welcome!
3 > OP+OQ+OR = 2(OP+OQ+OR)/2 > (PQ+QR+RP)/2 = (AB+BC+CA)/4 = 2 ?
@Anonymous not sure I follow you. Can you please elaborate?
By the triangle inequality and the mid-pt theorem, OP+OQ>PQ and PQ = AB/2. Then, 2 < OP+OQ+OR < 3 ??
19:45
$OP + OQ \gt PQ$ yes and $PQ = AB/2$ yes but how does that lead to $OP + OQ + OR \gt 2$? All we know is $OP + OQ + OR \gt OR + AB/2$
I'm not sure whether I'm right or not. We can use the triangle inequality (3 times) and mid-pt theorem (3 times). OP+OQ+OR = 2(OP+OQ+OR)/2 = [(OP+OQ) + (OQ+OR) + (OR+OP)]/2 > (PQ + QR + RP)/2 = (AB/2 + CA/2 + BC/2)/2 = (AB+BC+CA)/4 = 8/4 = 2
you are absolutely right and that is a very good catch
@petaarantes please see comments from Anonymous. There is a stronger lower bound on the value of $OP + OQ + OR$ than what I have in my answer. So it seems there is no integer value possible for $OP + OQ + OR$. Can you please unaccept my answer? I would like to delete it.
@Anonymous you may want to add an answer showing no integer value is possible.

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