Q.1
14 MarksAn integral with an infinite limit is called an improper integral. It converges if its value is a finite number.
Replace the upper limit by and take the limit .
Use .
The value is finite.
The integral converges, and its value is .
Gamma function: for , the gamma function is defined as
Two properties are used here:
- when is a positive integer
Evaluation: write the given integral in the form of the definition.
Comparing with the definition, .
The upper half of the circle is the curve , from to . Rotating it about the x-axis gives a sphere of radius .
y
| y = sqrt(r^2 - x^2)
. | .
. | .
. | y .
---+------+------+--- x
-r 0 rCut the sphere by a plane at a distance from the centre. The slice is a thin disc of radius and thickness .
Add all slices from to . This is the disc method.
From the circle, .
The function is even, so the integral from to is twice the integral from to .
The volume of the sphere is cubic units.