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Calculus Help

  1. Sep 30, 2004 #1
    I done these problems, can anyone tell me if it's right or wrong? Thanks :smile:

    1) Compute lim (as x approaches 2) of (3x sin(pi x) + cos (pi x))
    I got: 1

    2) Use the derivative rule to find 1/(x-4)
    I got: -1/((x+h-4)(x-4))

    3) Find an equation for the tangent line to the graph given by:
    2x^2 + xy - 4y^2 = 2
    at the point where (x,y) = (2, -1)

    I got: y = -(7/10)x + (2/5)

    4) A 5 foot girl is walking towards a 24 foot lamppost at the rate of 7 feet per second. At what speed is the tip of her shadow moving when she is 8 feet from the lampost?
    I got: (168/19) feet per second
  2. jcsd
  3. Sep 30, 2004 #2
    first three questions seem ok to me.
    The second answer is the limit for h to zero of your solution devided by h. Ofcourse if you just apply the standard rules you get : -1/(x-4)²

    i don't get your fourth question though...
  4. Sep 30, 2004 #3


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    I got the same number you did for problem 4 on my first pass.
  5. Sep 30, 2004 #4
    hi Buff,

    Yes, yes, yes, got the same answer for question four...

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