हिंदी
Tamil Nadu Board of Secondary EducationHSC Commerce Class 12

Definite Integrals

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Estimated time: 9 minutes
CBSE: Class 12

Definition: Definite integral

A definite integral represents the value of a function accumulated between two limits.
It can also be interpreted geometrically as the net area between the graph of y = f(x) and the x-axis from x = a to x = b.

CBSE: Class 12

Indefinite vs definite integral

Feature Indefinite Integral Definite Integral
Notation \[\int f(x) \, dx\] \[\int_{a}^{b} f(x) \, dx\]
Result Function family Numerical value
Constant C Present Not present
Limits No limits Lower and upper limits
Meaning Antiderivative Net area / accumulated value
CBSE: Class 12

Example 1

Evaluate:

\[\int_{0}^{1} x \, dx\]

Solution: An antiderivative of x is \[x^2 / 2\]. So,

\[\int_{0}^{1} x \, dx = \left[ \frac{x^2}{2} \right]_{0}^{1} = \frac{1^2}{2} - \frac{0^2}{2} = \frac{1}{2}\]

Answer: 1/2

CBSE: Class 12

Example 2

Evaluate:

\[\int_{1}^{3} (2x + 1) \, dx\]

Solution: An antiderivative of \[2x + 1\] is \[x^2 + x\]. Hence,

\[\int_{1}^{3} (2x + 1) \, dx = [x^2 + x]_{1}^{3} = (9 + 3) - (1 + 1) = 10\]

Answer: 10

CBSE: Class 12

Real Life Examples

  • Distance from velocity: If velocity changes with time, a definite integral gives the total displacement over a time interval.

  • Economics: Total change can be obtained from a rate function, such as marginal quantity accumulated over a fixed interval.

  • Area measurement: Definite integrals help measure curved regions more accurately than ordinary geometry formulas.

CBSE: Class 12

Key Points: Definite Integrals

  • Used to find exact accumulated value over a fixed interval.

  • Written as \[\int_{a}^{b} f(x) \, dx\].

  • Evaluated using \[F(b) - F(a)\].

  • Gives a unique numerical value.

  • Represents net area geometrically.

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