F+F F R2 s F1+BR2=∑F F=E+F F FR2=F+F83=∑F F=Fmn+Fn=∑F=∑F1 1 2 F F F R = + = = + = 3 1 2 1 3 i FR FR FR Fi = + =  =  = − i ni FR FRn Fn Fi F 1 1 ... ... ... = = + = 3 1 2 1 3 i FR FR FR Fi FR1 F1 F2 = +