Theory of Machine
The relation l = (2/3).(j + 2) apply only to kinematic chains in which lower pairs are used. This may be used to kinematic chains in which higher pairs are used, but each higher pair may be taken as equivalent to

Two lower pairs and two additional links
Two lower pairs and one additional link
Any one of these
One lower pair and two additional links

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Theory of Machine
Angle of descent of cam is defined as the angle

During which the follower returns to its initial position
Through which the cam rotates during the period in which the follower remains in the highest position
Moved by the cam from the instant the follower begins to rise, till it reaches its highest position
Of rotation of the cam for a definite displacement of the follower

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