Question

Please help! 3(cos90° + i sin90°) dot (cos39°+ i sin39°)

Answer 1

i got to the step: 3(cos181° + i sin78°) I'm not sure if i should just add 181° and 78° together ?

Answer 2

i m getting -3sin39+3icos39

Answer 3

what?? -.-

Answer 4

can you please write out the steps ?

Answer 5

cos90=0 and sin90=1, therefore u get 3(0+i).(cos39+isin39)
3i(cos39+isin39)
now since i^2=-1, u get 3icos39+3i^2sin39
-3sin39+3icos39

Answer 6

oh my god I am soooo sorry, I wrote the problem wrong... it is 3(cos91 + i sin91) not 90 =.=

Answer 7

my fault so sorry :(

Answer 8

i was like so weird how the heck u get -3 :D

Answer 9

now i m getting cos130+isin130

Answer 10

is my answer correct?

Answer 11

the heck :D, is that the final answer ?

Answer 12

i got 3 cis 260° as the answer but I'm not sure :|

Answer 13

let me recheck my calculations

Answer 14

ok, but before i got 3 cis 260°. i got 3(cos182°+ i sin 78°) and i just added those two together to get 3 cis 260° but I;m not sure

Answer 15

can u tell me what does cis mean?

Answer 16

sorry,forgot 3, my final ans is 3(cos130+isin130)

Answer 17

(cos91+isin39).(cos39+isin39)=cos91cos39+i(sin91cos39+cos91sin39)-sin39sin91
now cos91cos39-sin91sin39=cos(91+39) and sin91cos39+cos91sin39=sin(91+39)
so you get cos130+isin130
multiply the above with 3, this is how i got to my answer

Answer 18

how did u get to ur ans?

Answer 19

yeah, got to know what cis means here
then my answer is 3cis130
but how did u get 182 and 78 and why did u add them?
u can't simply add them.. further cistheta=cos(theta)+isin(theta) since theta is the arguement of the complex number,it has to be the same in both cos and sin terms,
u cannot have one value of theta in a particlar term and another in the other term and there is no point in adding them the way u did