@book{73819,
	author = {Blackburn, Hugh,},
	title = {Elements of Plane Trigonometry :},
	publisher = {Project Gutenberg,},
	year = {2010},
	address = {Salt Lake City, UT :},
	note = {Release date is 2010-06-25},
	url = {https://www.gutenberg.org/ebooks/32973}
}