# Thread: [SOLVED] Cosine rule 2

1. ## [SOLVED] Cosine rule 2

If you could help me in any way it would be great!!! I accidently typed the wrong question!(I sometimes wonder how I got into this maths class=])
this is the right question:
A boat travels 6.3km due north and then turns 17degrees towards the west and travels a further 7.2kms. How far is it from it's initial position?

x^2=6.3^2+7.2^2-2(6.3)(7.2)cos17
x^2=91.53-90.72Xcos17
x^2=91.53-86.76
x^2=4.77
x=2.18

any help would be great! Thank you for taking the time to help me with my trig h/w!!

2. I think you should try this... ?!

$\displaystyle x^2=6.3^2+7.2^2-2(6.3)(7.2)cos(180\deg - 17\deg )$

3. Hello, xch3m_is_l0v3x!

You didn't make a sketch, did you?

A boat travels 6.3km due north . $\displaystyle {\color{blue}AB = 6.3}$
and then turns 17° towards the west . $\displaystyle {\color{blue}\angle NBC = 17^o}$
and travels a further 7.2kms. . $\displaystyle {\color{blue}BC = 7.2}$
How far is it from it's initial position?
Code:
    C *           N
\\         :
\ \ 7.2   :
\  \     :
\   \17°:
\    \ :
\     * B
\    |
\   |
\  | 6.3
\ |
\|
* A

Get it? . . . You should have used: $\displaystyle \angle ABC = 163^o$