Laws of Motion Part 1

Let the two forces be F1 and F2 and let F2 is smaller than F1 and assume R is the resultant force.
Given F1+F2=18 .....(i)
From the right angle triangle, F22+R2=F12
or F12−F22=R2
or (F1+F2)(F1−F2)=R2
or (18)(F1−F2)=(12)2=144
or (F1−F2)=8.....(ii)
By solving equation (i) and (ii) we get,
F1=13N and F2=5N