Cosine / sine item?

The Yacht Race start again consists of 3 legs 1st Leg, yacht sails 8.5 kilometers with an inclination of 65 degrees True North 2nd Stage, the yacht sails of 10 kilometers with an inclination of 290 degrees True North 3rd Stage, the yacht was hampered by rough seas and only can handle a speed 6km/hr How long is the final stage? Cheers guys

The triangle leg1, leg2, Leg3, has an angle of 45 degrees between leg1 and leg2 (using 65 degrees and 360-290 = 70 degrees, to carry 180 to see this). Use the cosine rule to the triangle formed by lengths of 10, 8.5 and angle 45 degrees between: – a ^ 2 = 10 ^ 2 +8.5 ^ 2-2 * 10 * 8.5 * cos 45 = 7.21 A 6km/hr, This will take 7.21 / 6 hours = 1.2 hours = 1 hour 12 minutes.

The New Racing Rules for Sailing 2009 Part 1