Question 1060290
<pre><b><font size = 4>
The word "cosine", "<u>CO</u> <u>SINE</u>", is an abbreviation for <u>CO</u>mplement's <u>SIN</u>e.

90°-x is the <u>CO</u>mplement of x, so sin(90°-x) is the 
<u>CO</u>mplement of x's <u>SIN</u>e, so 

sin(90°-x) equals cos(x).

Edwin</pre></b></font>