# bearings, triginometry

• Mar 11th 2009, 07:46 AM
Tweety
bearings, triginometry
Quote:

A helicopter flies on a bearing of 200° from A to B, where AB=70 km. It then flies on a bearing of 150° from B to C, where C is due south of A. Work out the distance of C from A.

can someone please tell me what is wrong with the diagram I have drawn?
• Mar 11th 2009, 08:30 AM
hairymclairy
The helicopter moves from A to B on a bearing of 200, so the point B should actually be on the other side of A as 200>180.You should end up with a triangle with C directly below A, where AB=70km. you then need to work out angles ABC and BCA so you can use the sine rule to find the length of AC.
• Mar 11th 2009, 08:54 AM
Soroban
Hello, Tweety!

Quote:

A helicopter flies on a bearing of 200° from \$\displaystyle A\$ to \$\displaystyle B\$, where \$\displaystyle AB = 70\$ km.
It then flies on a bearing of 150° from \$\displaystyle B\$ to \$\displaystyle C\$, where \$\displaystyle C\$ is due south of \$\displaystyle A\$.

Find the distance from \$\displaystyle C\$ to \$\displaystyle A.\$

The first leg of the flight looks like this:
Code:

```            :             :             :           A *           /  200°       70 /         /         /       /     B *```

The second leg looks like this:
Code:

```      :       :     B * 150°       :\       : \       :  \           \           \             * C```

So the diagram should look like this:
Code:

```      :          * A       :        * |       :  70  *20°|       :    *    |       :20°*      |       : *        |     B * 130°      |       : *        |       :30°*      |       :    *    |       :      *30°|       :        * |       :          * C```
• Mar 11th 2009, 09:20 AM
masters
Quote:

Originally Posted by Tweety
can someone please tell me what is wrong with the diagram I have drawn?

Hi Tweety,

See diagram. And see Soroban's post for the angles.