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9:30 .... Safari AA Q N 1 of 4 26 Fri 27 next Sun Forum Grapher Calculus II : 25 Parametric curves K Live Notes Expand All PDF-beta One of central themes in calculus is the study of the shapes of graphs of curves y = f(x). In this lesson we describe a new method for discribing curves by using a third variable called a parameter. Such descriptions are natural and they are common in physics. For example, each of the two coordinates of a particle moving in the plane an be given as functions of time. x = f (t), y = g(t). Example - The unit circle. O Consider familiar equations: x = cost, y = sint, 0