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Mathematics Dictionary
Dr. K. G. Shih


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Parametric Equation
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Q01. Parametric equation : x = tan(t) and y = sec(t)

Question 1 : Find coordiantes of the foci
  • Change to standard form of hyperbola
    • Since 1 + tan(t)^2 = sec(t)^2
    • If x = tan(t) and y = sec(t)
    • Then 1 + x^2 = y^2
    • Hence x^2 - y^2 = -1
    • This is a hyperbola with principal axis y = 0
  • Focal length f = Sqr(a^2 + b^2)
  • Center is at (0,0)
  • Vertices are at (0, 1) and (0, -1)
  • Foci are at (0, Sqr(2)) and (0, -Sqr(2))
Question 2 : Find the asymptotes
  • y = +x is the asymptote
  • y = -x is the asymptote
Note : Standard form of hyperbola
  • (x/a)^2 - (y/b)^2 = +1 with principal axis x = 0
  • (x/a)^2 - (y/b)^2 = -1 with principal axis y = 0
  • Focal length f = Sqr(a^2 + b^2)
Reference

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Q02. Parametric equation : x = sec(t) and y = tan(t)

Question 1 : Find coordiantes of the foci
  • Change to standard form of hyperbola
    • Since 1 + tan(t)^2 = sec(t)^2
    • If x = sec(t) and y = tan(t)
    • Then 1 + y^2 = x^2
    • Hence x^2 - y^2 = +1
    • This is a hyperbola with principal axis x = 0
  • Focal length f = Sqr(a^2 + b^2)
  • Center is at (0,0)
  • Vertices are at (1, 0) and (-1, 0)
  • Foci are at (Sqr(2), 0) and (-Sqr(2), 0)
Question 2 : Find the asymptotes
  • y = +x is the asymptote
  • y = -x is the asymptote
Note : Standard form of hyperbola
  • (x/a)^2 - (y/b)^2 = +1 with principal axis x = 0
  • (x/a)^2 - (y/b)^2 = -1 with principal axis y = 0
  • Focal length f = Sqr(a^2 + b^2)
Reference

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Q03 Diagrams of unit circle and hyperbola

Find the parametric equations of unit hyperbola
  • 1. Find the curve of x = tan(t) and y = sec(t)
  • 2. Find the curve of x = cot(t) and y = csc(t)
  • 3. Find the curve of x = sec(t) and y = tan(t)
  • 4. Find the curve of x = csc(t) and y = cot(t)

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