References

Here you can find all the difficult topics well explained:

#	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
3.	Oscilloscope	http://en.wikipedia.org/wiki/Oscilloscope