In [1], the R⋅R⋅ Janic inequality is given by hb+hcra+hc+harb+ha+hbrc⩾23.
In [2], the inequality is strengthened to hb+hcrahc+harbha+hbrc⩾81
Here, ha,hb,hc,ra,rb,rc represent the altitudes and the radii of the excircles opposite to the sides a,b,c of △ABC, respectively.
Solution
⩽2bc2bcs(s−a)=s(s−a)
It can be known that rh+rc⩾2wc, Similarly, rc+ru⩾2wb,ru+rh⩾2wc. Thus, inequalities (3) and (4) can be strengthened to (rh+rcwa)λ+(rc+rawb)′+(ru+rhwc)λ⩽2λ3(λ∈R+)rh+rcwarc+rawbra+rhwc⩽81
This paper provides similar and strengthened versions of (1) and (2). ∵rb+rc=s−bs(s−c)(s−a)+s−cs(s−a)(s−b)⩾2s(s−a),(s=2a+b+c)ha=a2s(s−a)(s−b)(s−c)=s(s−a)⋅a1⋅2(s−b)(s−c)⩽as(s−a)[(s−b)+(s−c)]=s(s−a),∴rh+rc⩾2ha.
Similarly, we have rc+ru⩾2hb.ra+rh⩾2hc.
From this, it is easy to obtain the similar inequalities of (1) and (2): rb+rcha+rc+rahb+ra+rbhc⩽23rb+rcharc+rahbra+rhhc⩽81
Let the angle bisectors of △ABC at angles A, B, and C be wa, wb, and wc, respectively, where wa=b+c2bcs(s−a) - 16 -
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