Posted by TP on .
Could someone help me with this question
Write in polar form : sinx  i cosx
I've come up to this point, and it's wrong, can't someone please help?
=sin(pie/2x)icos(pie/2x)
=cosxisinx
=cis(x)
But the answer is cis(xpie/2)

Maths 
Reiny,
almost
sinx = cos(pi/2  x) and cosx = sin(pi/2  x)
that is, the sine of any angle equals the cosine of its compliment.
so sinx  i cosx
= cos(pi/2  x)  i sin(pi/2  x)
= cis(pi/2  x)
this webpage has some good examples with simple diagrams to show your topic
http://www.intmath.com/Complexnumbers/4_Polarform.php