Question

Y is inversely proportional to ?} " alt="x {3}^{?} " align="absmiddle" class="latex-formula">
y=44 when x=a
Find y when x=2a
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Answer 1

$\qquad \qquad \textit{inverse proportional variation} \\\\ \textit{\underline{y} varies inversely with \underline{x}} ~\hspace{6em} \stackrel{\textit{constant of variation}}{y=\cfrac{\stackrel{\downarrow }{k}}{x}~\hfill } \\\\ \textit{\underline{x} varies inversely with }\underline{z^5} ~\hspace{5.5em} \stackrel{\textit{constant of variation}}{x=\cfrac{\stackrel{\downarrow }{k}}{z^5}~\hfill } \\\\[-0.35em] \rule{34em}{0.25pt}$

$\stackrel{\textit{"y" is inversely proportiional to }x^3}{y = \cfrac{k}{x^3}}\qquad \textit{we also know that} \begin{cases} y = 44\\ x = a \end{cases} \\\\\\ 44 = \cfrac{k}{a^3}\implies 44a^3=k~\hfill \boxed{y=\cfrac{44a^3}{x^3}} \\\\\\ \textit{when x = 2a, what is "y"?}\qquad y = \cfrac{44a^3}{(2a)^3}\implies y = \cfrac{44a^3}{8a^3}\implies \blacktriangleright y = \cfrac{11}{2} \blacktriangleleft$