# cosθ-cosθ' = const. Bisector exact straight line #2

- Author:
- asifsound

Parent page is cosθ-cosθ' = const. exact straight line Linkage.
■ Changing from Antiparallelogram to Parallelogram
crank range 180° to 360° (in return stroke): After passing the

**shrunk**point, Antiparallelogram switched to Parallelogram form (same as Chebyshev case). ----- This restriction comes from GeoGebra poor function. Circle and circle 2 intersections criteria is somewhat odd. (a kind of bug (???) ) In real world , it will not occur perhaps.**To avoid this, Please introduce a variable flag ii as, intersect[k, p, ii] , ii = variable flag 1 or 2 dynamically.**■ point DDD traces exact straight line, by 7 bars. --- i.e. Exact Robert's straight line linkage has no merit. but, approximate Robert's line linkage has merit. This material's purpose is educational one / review.