R=(F12 + F22 - 2F1* F2 * COS (anlge between F1 and F2) )1/2
or
R=(F12 + F22 + 2F1* F2 * COS (anlge between F1 and F2) )1/2
both above equations are found in engineering mechanics books.
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/a_____180-a/a
Dear Dr. Kadhim,
I tried to draw the situation. One adds two forces via the parallelogram rule or via the chain rule. The "longer" diagonale is the resultant force in both case. So the sign before the cosinus function depends on whether the vectors start from one point (2) or they follow each other (1).
Thank you Dr. Éva Szőke for your answer, but I think when we assume that there are two collinear forces in the same direction (angle between them equal to zero) or in the opposite direction (angle between them 180), the second equation is suitable to calculate the resultant force.
Thank you Dr. Éva Szőke, and I am very grateful for your great interest in this question.
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