4. Integration: Basic Trigonometric Forms
by M. Bourne
In this section, we obtain the following integral formulas by reversing the formulas for differentiation of trigonometric functions that we met earlier:
We now apply the power formula to integrate some examples.
Example 1: Integrate: ![]()
Example 2: Integrate: 
Integral formulas for some other trigonometric functions: (These are obtained by just reversing the differentiation process).
Example 3: Integrate: ![]()
NOTE: The above formulas were obtained by reversing the differentiation process.
Further Integrals
Now, if we want to find
, we
note that


Similarly, it can be shown that
Hence, we can summarise that :
Example 4: Integrate: ![]()
Example 5: Integrate: 
Example 6: Find the area under the curve of
y = sin x from
x = 0 to
.
Exercises
Integrate each of the given functions:
1. 
2. 
3. If the current in a certain electric circuit is i = 110 cos 377t, find the expression for the voltage across a 500-μF capacitor as a function of time. The initial voltage is zero. Show that the voltage across the capacitor is 90° out of phase with the current.
We need the following result from electronics, which gives the voltage across a capacitor, where C is the capacitance:
4. A force is given as a function of the distance from the origin as
Express the work done by this force as a function of x if W = 0 for x = 0.
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