Question

If the value of "y" varies directly with "x"
and y =-8 when x=4.
Find "y" when x =-4.
Please show work if you want a brainiest!!

Answer 1

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

$\stackrel{\textit{"y" varies directly with "x"}}{y=kx}\qquad \qquad \textit{we also know that} \begin{cases} y=-8\\ x = 4 \end{cases}\implies -8=k(4) \\\\\\ \cfrac{-8}{4}=k\implies -2=k ~\hfill therefore~\hspace{10em}\boxed{y=-2x} \\\\\\ \textit{when x = -4 what is "y"?}\qquad y=-2(-4)\implies y=8$

Answer 2

Answer:

y=8

Step-by-step explanation:

I didn't need a equation if they vary directly with each other then if the sign switches from 4 to -4 then -8 must have switched to 8