Chapter 7 - Applications of Trigonometry and Vectors - Section 7.4 Vectors, Operations, and the Dot Product - 7.4 Exercises - Page 330: 55

The magnitude of the resultant force is 24.4 lb

Let $a = 15~lb$ Let $b = 25~lb$ Let angle $\theta = 110^{\circ}$ We can use the parallelogram rule to find $c$, the magnitude of the resultant force: $c = \sqrt{a^2+b^2+2ab~cos~\theta}$ $c = \sqrt{(15~lb)^2+(25~lb)^2+(2)(15~lb)(25~lb)~cos~110^{\circ}}$ $c = \sqrt{593.48~lb^2}$ $c = 24.4~lb$ The magnitude of the resultant force is 24.4 lb