Question 975042
If 180° < &#952; < 270° and sin&#952; = p, express cos&#952; in terms of p.
<pre>
180° < &#952; < 270° means that &#952; is in Quadrant III, in which quadrant
tan&#952; is positive, cos&#952; and sin&#952; are both negative, so the answer will
be a negative number.

A well-known identity is

sinē&#952; + cosē&#952; = 1               <--We solve for cos&#952;:

        cosē&#952; = 1 - sinē&#952; 
                  _________ 
         cos&#952; = ą&#8730;1 - sinē&#952;

Since we know that the answer will be negative we
use only the negative sign, and substitute p for sin&#952;.
     
                  ______ 
         cos&#952; = -&#8730;1 - pē
         
Edwin</pre>