Why is making two corners round slower than make all corners round?

Why is making two corners round slower than make all corners round?

References

Reference NO 1

http://stackoverflow.com/questions/15192975/why-is-making-two-corners-round-slower-than-make-all-corners-round

Reference NO 2

http://stackoverflow.com/questions/16165296/uibezierpath-does-not-draw-rounded-bottom-corners

Reference NO 3

http://stackoverflow.com/questions/6876761/how-to-remove-sharp-rectangle-edges-from-uibutton-control

Reference NO 4

http://stackoverflow.com/questions/4847163/round-two-corners-in-uiview

Reference NO 5

http://msdn.microsoft.com/en-us/library/ie/gg589503(v=vs.85).aspx

Reference NO 6

http://idiotsguides.com/static/quickguides/automotive/learning-to-ride-taking-turns-and-corners-on-your-motorcycle.html

Reference NO 7

http://fireworks.smashingmagazine.com/2012/05/07/refining-designs-adobe-fireworks/

Reference NO 8

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