Theory of Machine
The driving and driven shafts connected by a Hooke's joint will have equal speeds, if

cosθ = sinα
cotθ = cosα
tanθ = ± cosα
sinθ = ± tanα

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Theory of Machine
Open pairs are those which have

Elements of pairs not held together mechanically
Two elements that permit relative motion
Point or line contact between the two elements when in motion
Surface contact between the two elements when in motion

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