Trigonometry question

catching_streams

Hi,
Can anybody tell me the formula for getting an angle A when I have the lengths of the 3 sides of a triangle. Ive forgotten how to do it. Its in relation to determining the reference angle A for converting complex numbers to their polar forms.
Cheers

joe.

a2 = b2 + c2 -2ab(cos c)

if i remember correctly

ecksor

Cosine rule.

a^2 = b^2 + c^2 - 2(bc)cosA where a is the length of the side opposite A.

ecksor

What do you mean by reference angle? You can convert complex numbers to polar form in a more striaghtforward manner by getting the angle from sin^-1(Im(z)/Re(z)).

ecksor

Er, tan^-1 I mean. It'd be sin^-1(Im(z)/sqrt(Im(z)^2 + Re(z)^2))

joe.

and thats in 2nd year right

ecksor

2nd year of what?

joe.

eh acting school

ecksor

Your sarcasm is electrifying, but complex numbers are studied in lots of different subjects and courses.

joe.

OK boss man

catching_streams

cheers lads,
so what i gather is im using these rules.
Re z = (z+z*)/2
Lm z = (z-z*)/zi
Im having trouble completing these two z = 0 + i2, z = -3 -i4
using this
sin^-1(Im(z)/sqrt(Im(z)^2 + Re(z)^2))
..must brush up on my complex numbers
...much appreciated

ecksor

totalfreeloader wrote:

cheers lads,
so what i gather is im using these rules.
Re z = (z+z*)/2
Lm z = (z-z*)/zi

Correct, assuming that z* means the conjugate of z.

Im having trouble completing these two z = 0 + i2, z = -3 -i4
using this
sin^-1(Im(z)/sqrt(Im(z)^2 + Re(z)^2))
..must brush up on my complex numbers
...much appreciated

What exactly are you trying to "complete" ? Are you trying to add them like vectors or is it something else?

The original post suggests that you're trying to find the angle between them, in which case it's far simpler to get the angle of each and subtract them. The formula I gave should give you the angle that each makes with the positive real line.