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Yr 12 Maths 1 Help

  1. Apr 4, 2005 #1
    Im havin some real problems with my maths :( I am behidn coz I went on a holiday for easter. I have a test tomorrow and I really need help :frown:

    If anyone could teach me how to do these sort of questions it would be much appreciated.

    1. Find all points of contact of horizontal tangents to the curve
    y=2√x+1/√x

    2. Find equation of tangent to
    y=1-3x+12x²-8x³
    which is parallel to the tangent at (1,2)

    3. The normal to the curve
    y=a√x+b/√x
    where a and b are constants, has equation 4x+y=22 at the point where x=4. Find the values of a and b.

    I havent had much trouble with other work in the chapter, but I have continously got questions similar to this wrong. Some help would be much appreciated.
     
  2. jcsd
  3. Apr 4, 2005 #2
    1. [tex] y'=0 [/tex]

    The solve for x.

    2. [tex] y'(1) = y' (x) [/tex]

    Find x.

    3. 4x+y=22, from which k=-4, from which [itex] k_t=1/4 [/itex] From which [itex] y' (4) = 0.25. [/itex]

    Edit:

    In 2. After you find the point of interest. Find the value of the derivative there, this will equal k (y=kx+l) of the tangent. It is simple then to find l.
     
    Last edited: Apr 4, 2005
  4. Apr 4, 2005 #3
    I dont quite understand 2 :(

    and where do u get k from?!
     
  5. Apr 4, 2005 #4
    I dont quite understand 2 :(

    Edit:eek:ops soz, ment to edit and get rid of the part where I said "where do u get k from"

    Edit2: aw crap, I still have no idea for those questions
     
    Last edited: Apr 4, 2005
  6. Apr 4, 2005 #5
    The k (y=kx+l) of a tangent of a curve at a certain point is equal to the value of the derivative of the curve at that point. After solving the equation, you will get an x or two that satisfy it. Find the value of the derivative at those points. Find the l's by satisfying that the tangents intersect with the curve at that point.
     
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