## anonymous 5 years ago expresss complex number in rectangular form $\sqrt{7}*cis*2.1$

1. anonymous

is that cosine ?

2. anonymous

its cis cos+isin

3. anonymous

yes it is stupid notation for $cos(\theta)+i sin(\theta)$

4. anonymous

im trying square of 7 which is 2.64 times cos but cos(?)

5. anonymous

i also assume that you are working in radians, not degrees. So just use a calculator. $\sqrt{7} [cos(2.1)+i sin(2.1)]$

6. anonymous

i get -1.336 for a and 2.284 for b (rounded) so answer is -1.336 + 2.284 i

7. amistre64

the cosine part relates to the x coord; the i sin part relates to the y coord right?

8. amistre64

Did the others parse it tight to be: cos(2.1) + i sin(2.1)?

9. amistre64

(-1.34, 42.30) is what i get with radian measurements...

10. amistre64

2.28.. musta hit a wrong buttononthe calc :)

11. anonymous

yes cosine is x and sine is y, usually written as a and b as in a + bi. I doubt it is (-1.34,42.3) for two reasons: the rectangular form of a complex number is a number, not a coordinate. so it should look like a + bi also we know that the absolute value of that number is $\sqrt7$

12. amistre64

correct, its similar to polar coordinates in that respect. But i think the exercise here is to see that complex numbers are nothing new and that they can be plotted in the same manner as rectangular coords...right?