Just saw the problem on the Mathematica Blog and followed the Mathematica Demo at http://demonstrations.wolfram.com/TheRadiiOfFourIncircles/ So I wondered why it was true. Placing the radii of the incircles to the tangent points on BC and using similar triangles makes it clear: r/BC=r1/BE =r2/EG =r3/GC=(r1+r2+r3)/(BE+EG+GC). Since (BE+EG+GC=BC), r = r1+r2+r3.
Just saw the problem on the Mathematica Blog and followed the Mathematica Demo at
ReplyDeletehttp://demonstrations.wolfram.com/TheRadiiOfFourIncircles/
So I wondered why it was true. Placing the radii of the incircles to the tangent points on BC and using similar triangles makes it clear:
r/BC=r1/BE =r2/EG =r3/GC=(r1+r2+r3)/(BE+EG+GC).
Since (BE+EG+GC=BC), r = r1+r2+r3.