Basic problem on force vectors

Question

Two equal forces with magnitude F act on a box by an angle of 120 degrees. Find the magnitude of the resultant force.

(The answer is F)

Answer 1

Use the formula for resultant force

R² = F1² +F2 ² + 2 F1 *F2 Cos Theta , Theta is angle between F₁ and F₂

Here F1 = F2 = F , Cos Theta = Cos 120 = -1/2

R² = F² +F ² - F² = F²

R = Resultant = F