Basic Integrals
Lesson · Beginner
Calculus
Definition (Signed Area)

The definite integral represents the signed area between the graph of f(x) and the x-axis.
Basic Properties
Common Antiderivatives
Evaluate
An antiderivative is
Therefore
Evaluate
The function
is odd:
Therefore the areas on opposite sides of the y-axis cancel.
Hence
Suppose
Evaluate I.
Write
Therefore
so
Suppose
Find
Let
Also,
Therefore, integrating the given equation,
Thus
so
Evaluate
Replace x by π/2 − x.
Then
Add the two expressions:
Therefore
Hence
If
on [a,b], then the area between the curves is
That is,
The average value of f on [a,b] is
If
for every x ∈ [a,b], then
More generally, if
then
Signed area:
Total geometric area between the graph and the x-axis:
An indefinite integral represents a family of antiderivatives:
A definite integral is a number:
so we do not add +C.
A region below the x-axis contributes negatively.
If the geometric areas are S, T, U as in your diagram,
not
For an indefinite integral, ∫f(x) dx always includes the constant of integration.
Do not write
The correct formula is
The power rule excludes n = −1.
Instead,
For example,
and