The resultant of two forces of 1120 N and 2210 N is 2870 N. What angle does the resultant make with each of the two forces?
Draw a triangle ABC with
AB = 1120
BC = 2210
AC = 2870
You want angles CAB and ACB. In other words, angles A and C
using the law of cosines,
2820^2 = 1120^2 + 2210^2 - 2(1120)(2210) cosB
Now, knowing cos B,
sinA/2210 = sinB/2870 = sinC/1120
sinA = 2210*sinB/2870
sinC = 1120*sinB/2870
Done.