Problem 3.3

จาก \(|\vec{A} + \vec{B}| = \sqrt{|\vec{A}|^{2} + |\vec{B}|^{2} + 2|\vec{A}||\vec{B}|\cos \theta}\)

\(|\vec{F}_{1} + \vec{F}_{2}| =\sqrt{|\vec{F}_{1}|^{2} + |\vec{F}_{2}|^{2} + 2|\vec{F}_{1}||\vec{F}_{2}|\cos \theta}\)

\(|\vec{F}| =\sqrt{(1 N)^{2} + (3 N)^{2} + 2(1 N)(3 N)\cos (30º)}\)

\(|\vec{F}| =\sqrt{1 + 3 + 3}N\)

\(|\vec{F}| =7N \;\blacksquare\)