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Using Trig Identities to see if derrivatives are equal

  1. Oct 17, 2009 #1
    1. The problem statement, all variables and given/known data
    for homework we have to find 2 different dirrivatives of the same problem (one may be incorrect) and then tell if they are equal

    2. The attempt at a solution
    original
    y=sec(x)*cot(x)

    the two derrivatives (i know these are correct becase i have compared with others in the class)

    using product rule first
    dy/dx=-sec(x)*cot^2(x)

    using simplification first
    dy/dx=-csc(x)*cot(x)

    this is my question......is there any way u can find that -secx(cotx)^2=-cscxcotx ??
     
  2. jcsd
  3. Oct 17, 2009 #2

    jgens

    User Avatar
    Gold Member

    Sure. You should know that sec(x) = 1/cos(x) and that cot(x) = cos(x)/sin(x). Using these definitions we have that sec(x) * cot2(x) = (1/cos(x)) * (cos2(x)/sin2(x)) = . . .
     
  4. Oct 18, 2009 #3
    Thx jgens!!! Ur a life saver
     
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