# Implicit Differentiation Formula

Implicit differentiation is the procedure of differentiating an implicit equation with respect to the desired variable x while treating the other variables as unspecified functions of x.

To differentiate an implicit function, any of the following methods is followed :

• In the first method, the implicit equation is solved for y and it is expressed explicitly in terms of x and differentiation of y is carried. This method is found useful only when y is easily expressible in terms of x.
• In the second method, y is thought of as a function of x, and both members of the implicit equation are differentiated w.r.t x. The resulting equation is solved to find the value of $\frac{dy}{dx}$ .

Solved Examples

Question 1: Calculate the implicit derivative of $x^{2}-5xy+3y^{2}=7$ ?

Solution:

Given implicit function is,
$x^{2}-5xy+3y^{2}=7$

$2x-\left(5x\frac{dy}{dx}+5y\right)+6y\frac{dy}{dx}=0$

$2x-5x\frac{dy}{dx}-5y+6y\frac{dy}{dx}=0$

$\frac{dy}{dx}\left(-5x+6y\right)=-2x+5y$

$\frac{dy}{dx}=\frac{-2x+5y}{-5x+6y}$

$\frac{dy}{dx}=\frac{2x-5y}{5x-6y}$

#### Practise This Question

When a certain metal was irradiated with light of frequency 1.6 × 1016 Hz, the photoelectrons emitted had twice the kinetic energy as the photoelectrons emitted when the same metal was irradiated with light of frequency 1.0 × 1016 Hz. Calculate the threshold frequency (v0) for the metal.