The vectors a and b represent two forces acting at the same point, and $\boldsymbol{\theta}$ is the smallest positive angle between a and b. Approximate the magnitude of the resultant force.
$$\|\mathbf{a}\|=2.0 \mathrm{Ib}, \quad\|\mathbf{b}\|=8.0 \mathrm{lb}, \quad \theta=120^{\circ}$$