How is the resultant of two like parallel forces obtained, using the theorem of moments ?

Explanation

Taking moments of forces P and Q about 'c' , we get `Pbar(AC)=Qbar(BC)`
moment of P about O=`Pbar(AO)`
Moment of Q about O=`Qbar(BO)`
Algebraic sum of moments of forces about O=`Pvar(AO)+Qbar(BC)`
`=P(AC+OC)+Q(OC-BC)`
`=Pbar(AC)+Pbar(OC)+Qbar(OC)+Qbar(BC)`
`=(P+Q)bar(OC)`
`:.Pbar(AO)+Qbar(BO)=Rbar(OC)`