Introductory Calculus from the Viewpoint of Non-Standard Analysis -   Derivative of Sine and Cosine
  This article exemplifies a novel approach to the teaching of introductory differential calculus using the modern notion of ``infinitesimal'' as opposed to the traditional approach using the notion of ``limit''. I illustrate the power of the new approach with a discussion of the derivatives of the sine and cosine functions. 
Jack L. Uretsky