Let the smaller force be of the magnitude F Newton
90° is the angle made by the resultant force with the smaller force
The angle between the resultant force and the larger force = (120° – 90°) = 30°
\(tan\;30^{\circ}=\frac{F\times sin\;120^{\circ}}{40+F\times cos\;120^{\circ}}\) \(\frac{1}{\sqrt{3}}=\frac{F\times \frac{\sqrt{3}}{2}}{40+F\times \frac{-1}{2}}\)80 – F = 3F
4F = 80
F = 20N
