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Let f:D\subset X-> X and there exists some x belongs to D such that )(x)={x,fx,f^{2}x,..}\subset of D. O(x) is orbit of x. Explain this plz? Combinatorics? A particle executes a SHM of time period R find time taken by particle go to directly from it s mean position to half the amplitude? How do you find an inverse demand curve? 2 times 2?