How do you find dy/dx by implicit differentiation of x^3+y^3=4xy+1 and evaluate at point (2,1)?

1 Answer
Oct 27, 2017

8/5

Explanation:

d/(dx)(x^3+y^3=4xy+1)--(1)

we will differentiate wrt" "x. Remembering that when differentiating y we multiply by (dy)/(dx) by virtue of the chain rule. Also on the RHS we will need the product rule on the first term

(1)rarr3x^2+3y^2(dy)/(dx)=4y+4x(dy)/(dx)+0

rearrange for (dy)/(dx)

3y^2(dy)/(dx)-4x(dy)/(dx)=4y-3x^2

(dy)/(dx)(3y^2-4x)=4y-3x^2

=>(dy)/(dx)=(4y-3x^2)/(3y^2-4x)

:.[(dy)/(dx)]_(color(white)(=)(2,1))=(4xx1-3xx2^2)/(3xx1^2-4xx2

=(4-12)/(3-8)=-8/-5=8/5