If y varies directly with x, if y=12 when x=18, how do you find x when y=-16?

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Answer 1 · 2016-01-01T16:59:50

$color(blue)(x=-24$ , when y =-16

$y$ varies directly with $x$ this implies that as $x$ increases $y$ increases too.

Let us introduce constant of proportionality $color(blue)(k$

$y=color(blue)(k)x$

$color(blue)(k)=y/x$

We have been provided with values for $x$ and $y$
$color(blue)(k)=12/18$

$k=2/3$ , this value stays constant.

So when $y=-16$

$x=y/k$

$x=-16/(2/3)$

$x=(-16 xx 3)/2$

$x=(-48)/2$

$color(blue)(x=-24$