Differentiation of Implicit Function

In this page differentiation of implicit function we are going to see some examples to understand where we have to apply this method.

Definition of implicit function:

When the relation between x and y is given by an equation in the form of f(x,y) = 0 and the equation is not easily solvable for y, then y is said to be implicit function.

Example 1:

Find dy/dx when x⁴ + 5 xy + y⁴ = 2

Solution:

Differentiating with respect to x on both sides

4x³ + 5 [x (dy/dx) + y (1) ] + 4 y³ = 0

4x³ + 5[x (dy/dx) + y ] + 4 y³ = 0

4x³ + 5x (dy/dx) + 5y + 4 y³ = 0

5x (dy/dx)  = -4x³ - 5y - 4 y³

dy/dx  = (-4x³ - 5y - 4 y³)/5x

dy/dx  = -(4x³ + 5y + 4 y³)/5x

dy/dx  = -(4x³/5x + 5y/5x + 4 y³/5x)

dy/dx  = -(4x²/5 + y/x + 4y³/5x)

differentiation of implicit function

Example 2:

Find dy/dx when y tan x  - y² cos x + 2x = 0

Solution:

Differentiating with respect to x

y (sec² x) + tan x (dy/dx) - [ y² (- sin x) + cos x (2y)(dy/dx) ] + 2 (1) = 0

y sec² x + tan x (dy/dx) - [ - y²  sin x + 2y cos x (dy/dx) ] + 2  = 0

y sec² x + tan x (dy/dx) + y²  sin x - 2y cos x (dy/dx) + 2  = 0

tan x (dy/dx) - 2y cos x (dy/dx) = -y sec² x - y²  sin x - 2

tan x (dy/dx) - 2y cos x (dy/dx) = -[y sec² x + y²  sin x + 2]

dy/dx [tan x - 2y cos x] = -[y sec² x + y²  sin x + 2]

dy/dx = -[y sec² x + y²  sin x + 2]/[tan x - 2y cos x]

Related Topics

Quote on Mathematics

“Mathematics, without this we can do nothing in our life. Each and everything around us is math.

Math is not only solving problems and finding solutions and it is also doing many things in our day to day life.  They are:

It subtracts sadness and adds happiness in our life.

It divides sorrow and multiplies forgiveness and love.

Some people would not be able accept that the subject Math is easy to understand. That is because; they are unable to realize how the life is complicated. The problems in the subject Math are easier to solve than the problems in our real life. When we people are able to solve all the problems in the complicated life, why can we not solve the simple math problems?

Many people think that the subject math is always complicated and it exists to make things from simple to complicate. But the real existence of the subject math is to make things from complicate to simple.”