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Topic
Reference
1.
Lissajous curve
http://en.wikipedia.org/wiki/Lissajous_curve
2.
Trigonometric functions
http://en.wikipedia.org/wiki/Trigonometric_function
3.
Sine wave
http://en.wikipedia.org/wiki/Sine_wave
Oscilloscope
http://en.wikipedia.org/wiki/Oscilloscope