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(%i1)rt:tan(atan(1/2)+atan(1/3))=1;
                                   1         1
(%o1)                     tan(atan(-) + atan(-)) = 1
                                   2         3
(%i2) trigsimp(lhs(rt));
                                     1         1
                            sin(atan(-) + atan(-))
                                     2         3
(%o2)                       ----------------------
                                     1         1
                            cos(atan(-) + atan(-))
                                     2         3
(%i3)  logarc(lhs(rt));
                    %i                %i             %i                %i
            %i (log(-- + 1) - log(1 - --))   %i (log(-- + 1) - log(1 - --))
                    2                 2              3                 3
(%o3) - tan(------------------------------ + ------------------------------)
                          2                                2
(%i4) ratsimp(%);
(%o4)             

mf:1=tan(atan(1/2)+atan(1/3));
                                       1         1
(%o1)                     1 = tan(atan(-) + atan(-))
                                       2         3
(%i2) trigsimp(rhs(mf));
                                     1         1
                            sin(atan(-) + atan(-))
                                     2         3
(%o2)                       ----------------------
                                     1         1
                            cos(atan(-) + atan(-))
                                     2         3
(%i3) logarc(rhs(mf));
                    %i                %i             %i                %i
            %i (log(-- + 1) - log(1 - --))   %i (log(-- + 1) - log(1 - --))
                    2                 2              3                 3
(%o3) - tan(------------------------------ + ------------------------------)
                          2                                2
(%i4) logcontract(exp);
(%o4)                                 exp
(%i5) ratsimp(%);
(%o5)              rectform(%);