102,79 = 7×1,05-1+108×(1+i2)-2 | - 7×1,05-1
102,79-7×1,05-1 = 108×(1+i2)-2 | * (1+i2)2
(1+i2)2 * (102,79-7×1,05-1) = 108 | : (102,79-7×1,05-1)
(1+i2)2 = 108/(102,79-7×1,05-1) | √
1+i2 = ±√(108/(102,79-7×1,05-1)) | -1
i2 = ±√(108/(102,79-7×1,05-1)) - 1