Question 1162459
<pre>
{{{drawing(800,160,-10,10,-2,2,

graph(800,160,-10,10,-2,2,cos(x),20,30,sin(x)),
line(pi/2,-.3,pi/2,-1),locate(pi/2-.1,-1,pi/2),
locate(pi,-1.1,pi),line(pi,-.3,pi,-1),
locate(-pi-.3,-1.1,-pi),line(-pi,-.3,-pi,-1),
line(-pi/2,-.3,-pi/2,-1),locate(-pi/2-.1,-1,pi/2),

locate(3pi/2-.2,-1.1,3pi/2),line(3pi/2,-.3,3pi/2,-1) 




)}}}

The red curve is of y = cos(x), the purple curve is of y = sin(x).

If we shift the purple (sine) curve left by &pi;/2 units, it will
coincide exactly with the red (cosine) curve.

That is to say 

{{{cos(x)=sin(x+pi/2)}}}


If we shift the purple (sine) curve right by 3&pi;/2 units, it will also
coincide exactly with the red (cosine) curve.

That is to say 

{{{cos(x)=sin(x-3pi/2)}}}
  

Edwin</pre>