1. http://www.intmath.com/trigonometric-graphs/4-graphs-tangent-cotangent-secant-cosecant.php
2. http://homepages.ius.edu/mehringe/M126/WebNotes%20sp%2009/Section%204.4%20Graphs%20of%20the%20Secant%20and%20Cosecant%20Functions.htm
3. http://www.brightstorm.com/math/trigonometry/trigonometric-functions/transforming-secant-and-cosecant
2. http://homepages.ius.edu/mehringe/M126/WebNotes%20sp%2009/Section%204.4%20Graphs%20of%20the%20Secant%20and%20Cosecant%20Functions.htm
3. http://www.brightstorm.com/math/trigonometry/trigonometric-functions/transforming-secant-and-cosecant