2. Contents:
1. Definition of integration as antiderivative
2. Rules of integration
3. Integration by substitution
4. Integration of composite function
5. Definition of definite integral
6. Properties of definite integral with simple problems
7. Area under the curve
8. Area bounded by two curves
3. 1. Definition of integration as antiderivative
Definition :
If
𝒅
𝒅𝒙
𝒇 𝒙 + 𝒄 =F(x) then 𝑭 𝒙 𝒅𝒙 = 𝒇 𝒙 + 𝒄 , where c is constant of integration
As
𝒅
𝒅𝒙
𝐜 = 𝟎
and 𝑭(𝒙)dx indicates integration of F(x) with respect to x
Symbol :
𝒅𝒙 𝒊𝒔 𝒐𝒑𝒆𝒓𝒂𝒕𝒐𝒓 𝒊𝒏𝒅𝒊𝒄𝒂𝒕𝒊𝒐𝒏 𝒊𝒏𝒕𝒆𝒈𝒓𝒂𝒕𝒊𝒐𝒏 𝒘𝒊𝒕𝒉 𝒓𝒆𝒔𝒑𝒆𝒄𝒕 𝒕𝒐 𝒙
Example :
𝒅
𝒅𝒙
𝒔𝒊𝒏𝒙 + 𝒄 =𝒄𝒐𝒔𝒙
hence, 𝒄𝒐𝒔𝒙 𝒅𝒙 = 𝒔𝒊𝒏𝒙 + 𝒄
8. 3. Integration by substitution
The first and most vital step is to be able to write your integral in this form:
Note This Step:
For example :
Here 𝑓 = 𝑐𝑜𝑠 and you have 𝑔 = 𝑥2
and its derivative of 2x
Now integrate:
∫cos(u) du = sin(u) + C
And finally put u= 𝒙 𝟐
back again:
sin(𝑥2
) + C
13. 6. Properties of definite integral with simple problems -2
• 7. Two parts
• 𝟎
𝟐𝒂
𝒇(𝒙) 𝒅𝒙 = 𝟐 𝟎
𝒂
𝒇(𝒙) 𝒅𝒙 … if f(2a – x) = f(x).
• 𝟎
𝟐𝒂
𝒇(𝒙) 𝒅𝒙 = 𝟎 … if f(2a – x) = – f(x)
• 8. Two parts
• −𝒂
𝒂
𝒇(𝒙) 𝒅𝒙 = 𝟐. 𝟎
𝒂
𝒇(𝒙) 𝒅𝒙 … if f(- x) = f(x) or it is an even function
• −𝒂
𝒂
𝒇(𝒙) 𝒅𝒙 = 𝟎 … if f(- x) = – f(x) or it is an odd function
14. 7. Area under the curve
• The area between the graph of y = f(x) and the x-axis is given by the definite
integral below. This formula gives a positive result for a graph above the x-axis,
and a negative result for a graph below the x-axis.
• Note: If the graph of y = f(x) is partly above and partly below the x-axis, the
formula given below generates the net area. That is, the area above the axis
minus the area below the axis.
15. Example of Area under the curve
• Find the area between y = 7 – x2 and the x-axis between the values x = –1 and x = 2.
16. 8. Area bounded by two curves
The area between the two curves or function is defined as the definite
integral of one function (say f(x)) minus the definite integral of other
functions (say g(x)).
• Thus, it can be represented as the following:
Area between two curves = 𝒂
𝒃
𝒇 𝒙 − 𝒈(𝒙) 𝒅𝒙