I1.3 Given that $\frac{1}{a}+\frac{1}{b}=\frac{Q}{a+b}$ and $\frac{a}{b}+\frac{b}{a}=R$, find the value of $R$.
$\begin{array}{l}\frac{1}{a}+\frac{1}{b}=\frac{4}{a+b} \\ \Rightarrow(a+b)^{2}=4 a b \\ \Rightarrow a^{2}+2 a b+b^{2}=4 a b \\ \Rightarrow a^{2}-2 a b+b^{2}=0 \\ \Rightarrow(a-b)^{2}=0 \\ a=b \\ \Rightarrow R=\frac{a}{b}+\frac{b}{a}=2\end{array}$