Don't know mathematica. Perhaps of interest, wolframalpha also fails to simplify to 0, see http://www.wolframalpha.com/input/?i=arccos%28-%287%2F9%29%29+-+2*arcsec%283... However my old maple 7 outputs 0 for simplify(arccos(-(7/9)) - 2*arcsec(3)); On Sun, Sep 28, 2014 at 6:13 PM, Bill Gosper <billgosper@gmail.com> wrote:

What is the "simplest" 0 FullSimplify can't see? Extra credit if FunctionExpand fails too. I'll start the bidding with

In[97]:= FullSimplify[FunctionExpand[Subtract @@ %]]

Out[97]= ArcCos[-(7/9)] - 2 ArcSec[3]

In[98]:= TrigExpand[Cos[%]]

Out[98]= 1 --rwg _______________________________________________ math-fun mailing list math-fun@mailman.xmission.com https://mailman.xmission.com/cgi-bin/mailman/listinfo/math-fun