O, Honorable Visitor,

This is the humble abode of Trig Frog, a small tutorial of the Sum and Difference Formulae and Multiple Angle Formulae of trigonometry. To the left thou shalt find links by which to navigate and learn. If thou art new to these formulae, Trig Frog suggests that thou start from the beginning and follow the links until thou hast completed the tutorial and tried thy hand at Trig Frog's Quiz. If thou only wishes a review of the Sum and Difference and Multiple Angle formulae, Trig Frog suggests that thou click the "Review" link at the bottom of the list, and then move on and test thy mettle at Trig Frog's Quiz. If at any time thou should wish to return to this friendly letter, please click on the proud, crowned frog in the top-right corner. He will direct thy browser's path.

~The Most Honorable Trig Frog

P. S. Because it is difficult to represent the square-root function on the internet, Trig Frog will use £, the symbol for the British unit of currency, to represent the square-root function in all the pages of this tutorial. So, £2 = sqrt(2).