Chapter 6 - Section 6.9 - Reciprocal Formulas Using a Calculator - Exercises - Page 261: 13

$R=318~\Omega$.

Given $\frac{1}{R}=\frac{1}{R_{1}}+\frac{1}{R_{2}}+\frac{1}{R_{3}}$ $R=80\Omega, R_{1}=175\Omega, R_{2}=275\Omega,R_{3}=?$ $\frac{1}{80}=\frac{1}{175}+\frac{1}{275}+\frac{1}{R_{3}}$ $\frac{1}{R_{3}}=\frac{1}{80}-(\frac{1}{175}+\frac{1}{275})$ Therefore, $R=318\Omega$ How to use the calculator: $80*x^{-1}-175*x^{-1}+275*x^{-1}=x^{-1}=$