Articles by W.L. Feldhusen W.L. FeldhusenW.L. Feldhusen is a mathematics educator in southern Vermont. They take particular interest in the history of mathematics teaching, the history of calculation, and in laboured geometric interpretations for straightforward bits of algebra. blog.willfeldhusen.com All articles by W.L. How do calculators do trigonometry?23 May 2019W.L. Feldhusen explains the obscure sine-finding trick hiding inside your calculator!