A = 1/a+1/b+c = b/ab + a/ab + abc/ab = (a + b + abc)/ab
B = 1/a - 1/b+c= = (b - a + abc)/ab
x/y : z/t = xt : yz = xt/yz ⇒
C = A : B = (a+b+abc)/(b-a+abc) = ((abc+b)+a)/((abc+b)-a)
abc+b = (-0,03)·3,56·6,41 +3,56 = - 0.684588 + 3,56 = 2,875412
C = (2,875412 +( -0,03))/(2,875412 - (-0,03)) =
= 2,845412/2,905412 ≈ 0,979348884 ≈ 0,979