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How is Δθ in circle equals to angle in velocity vectors triangle?
I tried using simple geometry but I can't.
That is not Vb in the figure on the right, that is -Vb(my mistake), so that dV = Va + (-Vb) ( vectors )photo : http://s613.photobucket.com/user/Yan_Wa_Chung/media/Untitled_zpsqfu6lfi8.png.html
you have to consider angle a and b in the figure on the left. And with some 90 degree usage:)