m · CA> + n · CB> = 0.

(2)

Hence if forces P, Q act in OA, OB, the resultant R will pass through C, provided

m = P/OA, n = Q/OB;

also

R = P·OC/OA + Q·OC/OB,

(3)

and

P · AC : Q·CB = OA : OB.

(4)