Shreya,
For this, suppose two forces are acting.
If the two forces (vectors) are acting in the same dirrection and the same sense, the angle between the two forces will be 0, so the maximum force will be reached at 0 degrees.
Illustration of the Example,
The inner product of the resultant force is
F1*F2=IF1I*IF2I*cos (F1,F2)
We are knowing that the maximum value of the IF1I*IF2I*cos (F1,F2) is given by the maximum value of the cos(F1,F2)=1 when the angle between F1 and F2 is 0 (180)
Sonash Askew