# Fallacies about the Derivative of the Trigonometric Sine Function

## TOH Tin Lam, TAY Eng Guan, and TONG Cherng Luen

#### National Institute of Education Nanyang Technological University Singapore

Published in The Mathematician Educator, 2021, Vol 2, No. 1, pp 1-10.

### Abstract

In this paper, several fallacies about the extension of the formula $\frac{d}{dx} (\sin x) = \cos x$ to the erroneous formula $\frac{d}{dx} (\sin x^\circ) = \cos x^\circ$ are discussed. In a Commognitive Theory Framework, misconceptions by ‘newcomers’ can be traced to the use of the word “unit”.