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Area of polar curve

  1. Oct 1, 2007 #1
    I've got a test tomorrow and I can't figure this one out:

    r[tex]^{2}[/tex] = 9cos(5[tex]\vartheta[/tex])

    I picked the inteval from 0 to [tex]\pi[/tex]/2 and I keep getting 18/5 but the back of the book says the answer is 18. I think something is wrong with my interval. Help Please!
  2. jcsd
  3. Oct 1, 2007 #2
    when the angle changed from 0 to pi/2 ,you DON'T get the whole curve!
    Try drawing out the curve.Note, cos(5*angle) must be > 0 to give a real point on the curve.

    when angle=0, r=3
    when angle=18 degree, r=0

    hope this is helpful
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