Britannica Educational Publishing 
Britannica Guide to Algebra and Trigonometry [PDF ebook] 

Calculating and manipulating the unknown has been the enterprise of the field of algebra since its earliest inception in Babylon and ancient Egypt. Trigonometry draws on principles presented in algebra and uses angle measurements to elaborate on geometric calculations. Essential to further mathematical and scientific study, both algebra and trigonometry provide crucial tools in managing variables and understanding the relationships between them. This volume presents the fundamentals of these fascinating areas of mathematics while chronicling their respective histories.