The vectors a and b represent two forces acting at the same point, and $\theta$ is the smallest positive angle between a and b. Approximate the magnitude of the resultant force.
$$\text { (a) } 20 \mathrm{lb}, \quad \mathrm{S} 17^{\circ} \mathrm{W} \quad \text { (b) } 50 \mathrm{lb}, \quad \mathrm{N} 82^{\circ} \mathrm{W}$$