Basic Concepts of Indefinite Integrals

As the differential coefficient of a constant is zero, we have

d/dx (F(x)) = f(x) ⇒ d/dx [F(x) + c] = f(x).

Therefore, ∫ f(x) dx = F(x) + c. This constant c is called the constant of integration and can take any real value.

Integration is the reverse process of differentiation. Two integrals of the same function can differ only by a constant. If integral of a function ‘A’ is ‘B’, then the differential of function ‘B’ is ‘A’. The indefinite integral of any function always has a constant. If integrand f(x) cab be written as the product of two functions f1(x) and f2(x) where f2(x) is a function of integral of f1(x), then put integral of f1(x) = t.

Basic Formulae

Some of the important integrals of some frequently used functions are listed below:

Some Standard Formulae

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Example 1: 

Evaluate ∫ 1/(1 + sin x) dx.

Solution:

In order to compute this integral, we multiply and divide it by (1-sin x) and so we have,

∫ 1/(1+ sin x) . (1 – sin x)/(1 - sin x) dx

= ∫ (1 – sin x)/(1 - sin²x) dx

= ∫ [(1 – sin x)/cos²x] dx

Now splitting it into two terms,

= ∫(1/cos²x dx – ∫ (sin x /cos²x) dx

=  ∫ sec²x dx – ∫ tan x sec x dx

= tan x – sec x + c.

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Example 2:

Evaluate ∫ sin x /(1 + sin x) dx.

Solution:

∫ sin x /(1 + sin x) dx

= ∫ (sin x + 1 – 1)/(1 + sin x) dx

= ∫1 –  ∫1/(1 + sin x) dx

= ∫1 – ∫(1 – sin x)/(1–sin² x) dx

= ∫1 dx –  ∫(1–sin x)/cos² x dx

= ∫(1 – sec² x + sec x tan x) dx

= x - tan x - sec x + C.

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Example 3: 

Evaluate ∫(sin³x + cos³x)/(sin²x cos²x) dx.

Solution: 

= ∫ tan x sec x dx + ∫ cot x cosec x dx 

= sec x – cosec x + c.
 

Methods of Integration

The following chart illustrates the various methods of integration:

 

These methods have been explained in detail in the coming sections. Students are advised to refer the coming sections to understand the concepts. Integration by substitution can further be divided into three parts:

 

It is better to memorize some of the standard substitutions as they often prove helpful in solving tricky questions.  

Q1. Integration is the inverse process of  

(a) the coefficient of x².

(b) anti differentiation

(c) differentiation

(d) anti derivative

Q2. The answer of an indefinite integral

(a) necessarily has a constant

(b) may or may not have a constant

(c) cannot have a constant

(d) none of these

Q3. The differential coefficient of a constant is

(a) number itself

(b) zero

(c) constant

(d) none of these

Q4. If ∫ f(x) dx = F(x) + c, then

(a) F(x) is called the primitive function of f(x).

(b) f(x) is called the primitive function of F(x).

(c) F(x) is called the derivative function of f(x).

(d) f(x) is called the root of F(x).

Q5. While solving integrals of the form x² + a² or √(x² + a²), the substitution used is

(a) x = a sec θ

(b) x = a tan θ

(c) x = a cosec θ

(d) x = a sin θ

Q1.	Q2.	Q3.	Q4.	Q5.
(c)	(a)	(b)	(a)	(b)

Related Resources

• You may wish to refer Integration by Substitution.

• Click here to refer the most Useful Books of Mathematics.

• For getting an idea of the type of questions asked, refer the previous year papers.