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## Homework Statement

A boat is sailing on a bearing of 120° and has a speed of 4ms^-1 relative to water. A current has a speed of 2ms^-1 and flows south west.

Find the resultant speed of the boat

**2. The attempt at a solution**

I've been stuck on this question for an hour now and can't figure out why I'm not getting the correct answer of 3.98ms^-1

If the current is going SW at 225°, (180°+45°), then i have the triangle vbc where b is 2ms^-1 and c is 4ms^-1 and the angle A=105° (225°-120°). (opposite the resultant velocity side v).

I then tried to use the cosine rule which gave me v=4.913...ms which i assumed should've worked.

can someone help me please, I've hit a brick wall again...