How to differentiate tan x?

Calculus can sometimes feel intimidating, but breaking down problems into manageable steps makes the process much easier. In this tutorial, we'll explore how to differentiate the tangent function, tan x, using two common methods: the quotient rule and trigonometric identities.

Understanding the Tangent Function

The tangent function is defined as the ratio of sine to cosine:

This expression will be very useful when we apply differentiation techniques.

Method 1: Using the Quotient Rule

The quotient rule is a formula for differentiating a function that is the quotient of two differentiable functions. Recall that if

then the derivative f'(x) is given by:

For tan x:

• Let g(x)=sin x (with derivative g'(x)=cos x).
• Let h(x)=cos x (with derivative h'(x)=-sin x).

Plugging into the quotient rule, we have:

Simplify the numerator:

Recall the Pythagorean identity:

Thus, the derivative simplifies to:

This is often written as:

Method 2: Using Trigonometric Identities

Another approach involves differentiating the tangent function directly, knowing that

While this result is usually provided as a standard derivative in calculus textbooks, understanding the derivation reinforces the concept. We can derive it by starting from the definition tan x = sin x/cos x​ and applying the quotient rule (as shown above). This method highlights the beauty of interconnected trigonometric identities.

Summary

To differentiate tan x, we:

1. Expressed tan x as sin x/cos x​.
2. Applied the quotient rule with sin x and cos x.
3. Simplified the expression using the Pythagorean identity to obtain sec^2 x.

Thus, we conclude: