Science and Mathematics for Engineering 6th Edition by John Bird

Exercise 17

$$\text { Evaluate resistance } \mathrm { R } \text {, given } \frac { 1 } { R } = \frac { 1 } { R _ { 1 } } + \frac { 1 } { R _ { 2 } } + \frac { 1 } { R _ { 3 } } \text { when } \mathrm { R } _ { 1 } = 3.6 \mathrm { k } \Omega , \mathrm { R } _ { 2 } = 7.2 \mathrm { k } \Omega \text { and } \mathrm { R } _ { 3 } = 13.6 \mathrm { k } \Omega$$