Editing Disc integration (section)

===Function of {{mvar|x}}===
If the function to be revolved is a function of {{mvar|x}}, the following integral represents the volume of the solid of revolution:

:<math>\pi\int_a^b R(x)^2\,dx</math>

where {{math|''R''(''x'')}} is the distance between the function and the axis of rotation. This works only if the [[axis of rotation]] is horizontal (example: {{math|''y'' {{=}} 3}} or some other constant).