Answer
$R=\dfrac{27.5}{\sqrt{x}}$
Work Step by Step
$R$ is inversely proportional to $\sqrt{x}$ so the equation that relates the variables is:
$R=\dfrac{k}{\sqrt{x}}$ where k = constant of proportionality.
If x = 121 , then $R = 2.5$. Substitute these values into the equation above to have:
$R=\dfrac{k}{\sqrt{x}}
\\2.5 = \dfrac{k}{\sqrt{121}}
\\2.5= \dfrac{k}{11}
\\2.5(11) = k
\\27.5=k$
The constant of proportionality is $27.5$. Thus, the equation that relates R and x is:
$R=\dfrac{27.5}{\sqrt{x}}$
