Ответ:

[tex] \frac{1}{r1.2.3} = \frac{1}{r1} + \frac{1}{r2} + \frac{1}{r3} = \frac{1}{15} + \frac{1}{15} + \frac{1}{15} = \frac{1}{45} \\ r1.2.3 = 0.022om \\ \frac{1}{r4.5} = \frac{1}{r4} + \frac{1}{r5} = \frac{1}{6} + \frac{1}{6} = \frac{1}{12} \\ r4.6 = 0.167om \\ r1.2.3.4.5.6 = r1.2.3 + r4.5 + r6 = 0.022 + 0.167 + 2 = 2.189om[/tex]