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ilikepie1234 ilikepie1234
wrote...
11 years ago
I am not understanding my textbook and I'm getting rather frustrated. Is there anyone who can break down implicit differentiation to something that I can understand?

Thanks. :]
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wrote...
11 years ago
Okay when you do implicit differentiation you're differentiating with respect to one variable... typically it's in respect of x... so if you took the derivative of y with respect to x you'd end up with dy/dx... so lets do a simple implicit differentiation...

With respect to x:

y^2 = 3x^2 + 2y

2y(dy/dx) = 6x + 2(dy/dx) (when you take the derivative of something with respect to another variable you have to tack on a dy/dx or whatever the variable is...

Another example...

With respect to y:

y^2 = 3x^2 + 5c^3 + 4e

2y = 6x(dx/dy) + 15c^2(dc/dy) + 4(de/dy)

Notice how whatever the variable is your deriving in respect to, it will always be d(whatever the variable is)...

I hope this helped out a bit... I know implicit differentiation can be a bit confusing...
ild
wrote...
11 years ago
Its called  " implicit "   because  we  usually  do  not  have a   "nice"     EXplicit  form  of  y=
   a  good  example is a  circle:
  x^2 +y^2 =25
   To  get  an  explicit  form    of y =  we   would  have to  break it into  two   functions,  neither of  which is   pretty,  and       find  y'   with   various  ?  forms ...  ugh!
   In    Implicit  differentiation,   we  know   a  relation  that    implies     this  circle : x^2 +y^2 =25
  and     there  are  4 steps  :

  a)  Differentiate  BOTh  sides   wrt  x,  using  chain  rule,  product rule,  etc
b)  collect  all  the  dy/dx  terms  on  one  side, all other terms  on  other
c)   factor out  the   dy/dx,   and  
d) Solve  for   dy/dx (  usually  by  dividing    by the   factor     in  c)

   I  usually  tell  MY  students  to include the  dx/dx term    even though it  becomes  1,  in  order to  make the  process  clear.
    Example :   What is the  slope of  the  circle ( above )  at (3,-4) ?
    Solution  :
  D(LS) = d(RS )
  so : d/dx (  x^2 +y^2)  =  d(25)/dx
 2x(dx/dx)  +2y(dy/dy)  =0  ( step  a)
 2y(dy/dx)  =-2x(dx/dx  ( step  b
    = -2x
   and  dy/dx  = -2x/2y   ( step  c,  d )

     and  now we  substitute in   ( x,y) = ( 3,-4)
   so   dy/dx = -2x/2y = -2(3)/2(4) = -3/4

 Advantages of Implicit :   faster,   simpler,  no  complex  forms, can  be used if  there is  NO  explicit  form ,    and   a " neater "  answer

   Disadvantages of implicit :  Need to  know product  rule,  chain  rule,   algebra   collecting, etc,  and  to   get  an  exact  numerical  answer  you   need to know  BOTH an  x  and  a  y  ON  the  curve . :
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