Problem 3.2

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

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

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

\(|\vec{F}| = F\sqrt{2(1 + \cos \theta )}\;\blacksquare\)