Question

How to know which is the angle from the x-axis of a vector with components (2 3)

Answer 1

Have you learnt the cosine rule?

Answer 2

nope

Answer 3

wait a sec :) please

Answer 4

I can say that, right?

Answer 5

Yep you can say that, but you really haven't learnt the law of cosines/cosine rule/cosine law?
(it has many names kay)

Answer 6

Not yet

Answer 7

Then you wouldn't be given this problem...

Answer 8

Here is the cosine rule: \(a^2=b^2+c^2-2bc\cos(A)\)
(a, b, c are sides of a triangle, and A, B, C are angles of a triangle)

Answer 9

does that help you?

Answer 10

Yep, thanks!

Answer 11

no problem :)

Answer 12

I dont know if my answer is correct, can you do it please?

Answer 13

what's your answer? :)

Answer 14

1.090

Answer 15

With this method I did this

Answer 16

4=9+13-2(3*sqrt13)(cosA)

Answer 17

oops, I did a mistake, give me a sec

Answer 18

ok :)

Answer 19

\[\frac{ -18 }{ -2(3\sqrt{13}) }=A\]

Answer 20

cos-1 of that

Answer 21

oh :(

Answer 22

don't give up :) try again :D

Answer 23

2/sqrt16 = cosA?

Answer 24

you mean 13

Answer 25

yep

Answer 26

and yes :)

Answer 27

Oh! got the same than with the first method!

Answer 28

So that is the angle x, and I need to do 2pi - this

Answer 29

?