# [SOLVED] Cosine rule 2

• Feb 10th 2009, 01:34 AM
xch3m_is_l0v3x
[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?(Headbang)

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(Angry)

any help would be great! Thank you for taking the time to help me with my trig h/w!!
• Feb 10th 2009, 01:44 AM
geld
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 )\$
• Feb 10th 2009, 04:38 AM
Soroban
Hello, xch3m_is_l0v3x!

You didn't make a sketch, did you?

Quote:

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\$