Monday, October 11, 2010

find dy/dx if y/x^3 + x/y^3 = x^2 y^4

Given the equation:


y/x^3 +
x/y^3 = x^2*y^4


We need to find
dy/dx


We will use implicit
differentiation.


First we will multiply both sides by
x^3*y^3


==> y^4 + x^4 = x^2 * y^4 * x^3 *
y^3


But we know that x^a *x^b =
x^(a+b)


==> y^4 + x^4 = x^5*
y^7


Now we will
differentiate.


==> 4y^3*y' + 4x^3 = (x^5)'*y^7 +
x^5*(y^7)'


==> 4y^3 y'+ 4x^3 = 5x^4 y^7 + 7x^5*y^6
*y'


Now we will combine terms with y' on the left
side.


==> 4y^3 y' - 7x^5 y^6 y' = 5x^4 y^7 -
4x^3


Now we will factor
y'.


==> y' (4y^3 - 7x^5 y^6) = (5x^4 y^7 -
4x^3)


Now we will divide
.


==> y' = ( 5x^4 y^7 - 4x^3) / (4y^3 - 7x^5
y^6)


==> y' =  x^3 ( 5xy^7 -4)/ y^3 (
4 - 7x^5 y^3)

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