Posted by **TP** on Wednesday, March 4, 2009 at 2:44am.

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/2-x)-icos(pie/2-x)

=cosx-isinx

=cis(-x)

But the answer is cis(x-pie/2)

- Maths -
**Reiny**, Wednesday, March 4, 2009 at 8:19am
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/Complex-numbers/4_Polar-form.php

## Answer This Question

## Related Questions

- CALC - 1. The problem statement, all variables and given/known data cos(x) = -2 ...
- Calc - 1. The problem statement, all variables and given/known data cos(x) = -2 ...
- physics - The motion of a particle is described by x = 10 sin (piet +pie/2 ). At...
- Math - What is the derivative of ((e^pie/3)(cosx))? Is it pie/3e^pie/3 times ...
- complex numbers! - -2-2i in polar form = 2.8 cis 2.35?? -3+4i polar form = 5 cis...
- Pre-Calc - Trigonometric Identities Prove: (tanx + secx -1)/(tanx - secx + 1)= ...
- MATHS...PLEASE HELP - Differentiate sin(cubed)x with respect to x. Hence find (...
- Precalculus/Trig - I can't seem to prove these trig identities and would really ...
- Trig........ - I need to prove that the following is true. Thanks (cosx / 1-sinx...
- Trigonometry. - ( tanx/1-cotx )+ (cotx/1-tanx)= (1+secxcscx) Good one! ...

More Related Questions