Definite Integral - Introduction
The definite integral is a fundamental concept in calculus.
It is a mathematical tool used to determine the area under a curve.
The definite integral measures the accumulation of a quantity over a given interval.
Definite Integral - Notation
The definite integral of a function f(x) from a to b is denoted as:
[ \int_{a}^{b} f(x) , dx ]
Definite Integral - Geometrical Interpretation
The definite integral represents the area enclosed between the curve and the x-axis.
The area can be positive, zero, or negative depending on the function and limits of integration.
Definite Integral - Properties
Property 1: Linearity - (\int_{a}^{b} (f(x) + g(x)) , dx = \int_{a}^{b} f(x) , dx + \int_{a}^{b} g(x) , dx)
Property 2: Constant Multiplication - (\int_{a}^{b} c \cdot f(x) , dx = c \cdot \int_{a}^{b} f(x) , dx)
Definite Integral - Properties (contd.)
Property 3: Reversal of Limits - (\int_{a}^{b} f(x) , dx = -\int_{b}^{a} f(x) , dx)
Property 4: Addition of Limits - (\int_{a}^{b} f(x) , dx + \int_{b}^{c} f(x) , dx = \int_{a}^{c} f(x) , dx)
Definite Integral - Properties (contd.)
Property 5: Integration of a Constant - (\int_{a}^{b} c , dx = c \cdot (b - a))
Property 6: Integration by Substitution - (\int_{a}^{b} f(g(x)) \cdot g’(x) , dx = \int_{g(a)}^{g(b)} f(u) , du)
Definite Integral - Properties (contd.)
Property 7: Integration by Parts - (\int_{a}^{b} u \cdot v’ , dx = u \cdot v \bigg|{a}^{b} - \int {a}^{b} v \cdot u’ , dx)
Property 8: Integration of a Function’s Derivative - (\int_{a}^{b} f’(x) , dx = f(x) \bigg|_{a}^{b} = f(b) - f(a))
Definite Integral - Example 1
Find (\int_{1}^{3} (2x - 3) , dx)
Solution:
Apply Property 1: (\int_{1}^{3} (2x - 3) , dx = \int_{1}^{3} 2x , dx - \int_{1}^{3} 3 , dx)
Integrate: ([x^2]\bigg|{1}^{3} - [3x]\bigg| {1}^{3})
Evaluate: ((9 - 1) - (9 - 3))
Definite Integral - Example 2
Find (\int_{0}^{2} (5x^2 - 4x + 1) , dx)
Solution:
Apply Property 1: (\int_{0}^{2} (5x^2 - 4x + 1) , dx = \int_{0}^{2} 5x^2 , dx - \int_{0}^{2} 4x , dx + \int_{0}^{2} 1 , dx)
Integrate: ([\frac{5}{3}x^3]\bigg|{0}^{2} - [2x^2]\bigg| {0}^{2} + [x]\bigg|_{0}^{2})
Evaluate: (\frac{5}{3}(8) - 2(4) + (2))
Definite Integral - Example 3
Find (\int_{1}^{2} \frac{2}{x^2} , dx)
Solution:
Apply Property 2: (\int_{1}^{2} \frac{2}{x^2} , dx = 2 \cdot \int_{1}^{2} \frac{1}{x^2} , dx)
Integrate: (2 \cdot [-\frac{1}{x}]\bigg|_{1}^{2})
Evaluate: (2 \cdot (-\frac{1}{2} + \frac{1}{1}))
Definite Integral - Example for Illustration of Property 1
Find (\int_{1}^{3} (2x - 3) , dx)
Apply Property 1: (\int_{1}^{3} (2x - 3) , dx = \int_{1}^{3} 2x , dx - \int_{1}^{3} 3 , dx)
Integrate: ([x^2]\bigg|{1}^{3} - [3x]\bigg| {1}^{3})
Evaluate: ((9 - 1) - (9 - 3) = 2)
Definite Integral - Example for Illustration of Property 2
Find (\int_{0}^{2} (5x^2 - 4x + 1) , dx)
Apply Property 2: (\int_{0}^{2} (5x^2 - 4x + 1) , dx = \int_{0}^{2} 5x^2 , dx - \int_{0}^{2} 4x , dx + \int_{0}^{2} 1 , dx)
Integrate: ([\frac{5}{3}x^3]\bigg|{0}^{2} - [2x^2]\bigg| {0}^{2} + [x]\bigg|_{0}^{2})
Evaluate: (\frac{5}{3}(8) - 2(4) + (2) = \frac{38}{3})
Definite Integral - Example for Illustration of Property 3
Find (\int_{1}^{2} \frac{2}{x^2} , dx)
Apply Property 3: (\int_{1}^{2} \frac{2}{x^2} , dx = -\int_{2}^{1} \frac{2}{x^2} , dx)
Integrate: (-2 \cdot [-\frac{1}{x}]\bigg|_{2}^{1})
Evaluate: (-2 \cdot (-\frac{1}{1} + \frac{1}{2}) = 2)
Definite Integral - Example for Illustration of Property 4
Find (\int_{1}^{3} 2x , dx + \int_{3}^{5} (4x - 1) , dx)
Apply Property 4: (\int_{1}^{3} 2x , dx + \int_{3}^{5} (4x - 1) , dx = \int_{1}^{5} 2x , dx)
Integrate: ([x^2]\bigg|_{1}^{5})
Evaluate: (25 - 1 = 24)
Definite Integral - Example for Illustration of Property 5
Find (\int_{3}^{6} 5 , dx)
Apply Property 5: (\int_{3}^{6} 5 , dx = 5 \cdot (6 - 3))
Evaluate: (5 \cdot 3 = 15)
Definite Integral - Example for Illustration of Property 6
Find (\int_{2}^{5} (3x - 2) \cdot 2 , dx)
Apply Property 6: (\int_{2}^{5} (3x - 2) \cdot 2 , dx = \int_{4}^{6} (u - 2) , du), where (u = 3x)
Integrate: (\int_{4}^{6} u , du - \int_{4}^{6} 2 , du)
Evaluate: ([\frac{1}{2}u^2]\bigg|{4}^{6} - [2u]\bigg| {4}^{6})
Definite Integral - Example for Illustration of Property 7
Find (\int_{1}^{4} x \cdot (2x - 3) , dx)
Apply Property 7: (\int_{1}^{4} x \cdot (2x - 3) , dx = [x^2 \cdot (x - \frac{3}{2})]\bigg|{1}^{4} - \int {1}^{4} x^2 \cdot 2 , dx)
Integrate: (x^2 \cdot (x - \frac{3}{2})\bigg|{1}^{4} - 2 \cdot \int {1}^{4} x^2 , dx)
Evaluate: ((64 \cdot (\frac{4}{2}) - \frac{81}{2}) - 2 \cdot [\frac{1}{3}x^3]\bigg|_{1}^{4})
Definite Integral - Example for Illustration of Property 8
Find (\int_{0}^{2} 3 , dx)
Apply Property 8: (\int_{0}^{2} 3 , dx = 3 \cdot (2 - 0))
Evaluate: (3 \cdot 2 = 6)
Definite Integral - Example for Illustration of Multiple Properties
Find (\int_{1}^{3} (2x^2 + 3x + 1) , dx + \int_{3}^{6} (4x - 2) , dx)
Apply Properties 1 and 4: (\int_{1}^{3} (2x^2 + 3x + 1) , dx + \int_{3}^{6} (4x - 2) , dx = \int_{1}^{6} (2x^2 + 3x + 1) , dx),
Integrate: ([\frac{2}{3}x^3 + \frac{3}{2}x^2 + x]\bigg|_{1}^{6})
Evaluate: ((\frac{2}{3}(216) + \frac{3}{2}(36) + 6) - (\frac{2}{3} + \frac{3}{2} + 1))
Definite Integral - Summary and Recap
The definite integral is a mathematical tool used to determine the area under a curve.
It has properties such as linearity, constant multiplication, reversal of limits, addition of limits, integration of a constant, integration by substitution, integration by parts, and integration of a function’s derivative.
Examples have been provided to illustrate these properties and the process of evaluating definite integrals.
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Definite Integral - Introduction The definite integral is a fundamental concept in calculus. It is a mathematical tool used to determine the area under a curve. The definite integral measures the accumulation of a quantity over a given interval.