Special Calculator

Quick demo

TeXForm[Result == ArcCosDegrees[(*FB[*)((((*SpB[*)Power[b(*|*),(*|*)2](*]SpB*) + (*SpB[*)Power[c(*|*),(*|*)2](*]SpB*) - (*SpB[*)Power[a(*|*),(*|*)2](*]SpB*)))(*,*)/(*,*)((2 b c)))(*]FB*)]]

.latex
\text{Result}=\cos ^{-1}\left(\frac{-a^2+b^2+c^2}{2 b c}\right)

Now the calculator

Module[{point = {1,1,1} 0.5},
Row[{  
  Manipulate[With[{r = ArcCosDegrees[(*FB[*)((((*SpB[*)Power[b(*|*),(*|*)2](*]SpB*) + (*SpB[*)Power[c(*|*),(*|*)2](*]SpB*) - (*SpB[*)Power[a(*|*),(*|*)2](*]SpB*)))(*,*)/(*,*)((2 b c)))(*]FB*)]},
    Row[{"Result = ", Re[r]}]
  ], {a, 0, 1, 0.1}, {b, 0, 1, 0.1}, {c, 0, 1, 0.1},
    ContinuousAction->True,
    "UpdateFunction" -> Function[{a,b,c},
        point = {a,b,c};
        True (* allow normal update *)
    ]
  ],

  Graphics3D[{
    ContourPlot3D[
      ArcCosDegrees[(*FB[*)((((*SpB[*)Power[b(*|*),(*|*)2](*]SpB*) + (*SpB[*)Power[c(*|*),(*|*)2](*]SpB*) - (*SpB[*)Power[a(*|*),(*|*)2](*]SpB*)))(*,*)/(*,*)((2 b c)))(*]FB*)], {a,0,1}, {b,0,1}, {c,0,1}, 
      PerformanceGoal->"Speed"][[1]],  
    
    {Directive[Red, "Emissive"->Red], Sphere[point // Offload, 0.05]}, 
    PointLight[Red, point // Offload, 1]}, 
  Axes->{True, True, True}, Boxed->True, AxesLabel->{"a","b","c"}] 
 }// Reverse ] 
]