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If y=7, when x=6, how do you find y when x=-21 given that y varies inversely as x?

1 Answer

Mar 19, 2017

$y = - 2$ $y=color(green)(-2)$

Explanation:

If $y$ $y$ varies inversely as $x$ $x$ then
$XXX x \times y = c$ $color(white)("XXX")x xx y=c$ for some constant $c$ $c$

We are told that $(x, y) = (6, 7)$ $(x,y)=(6,7)$ is a solution to the required relation;
so
$XXX 6 \times 7 = c XX \to XX c = 42$ $color(white)("XXX")6 xx 7 =c color(white)("XX")rarrcolor(white)("XX")c=42$

$XXXXXXXXXXX \to XX x \times y = 42$ $color(white)("XXXXXXXXXXX")rarrcolor(white)("XX")x xx y =42$

When $x = - 21$ $x=-21$
$XXX (- 21) \times y = 42 XX \to XX y = - 2$ $color(white)("XXX")(-21) xx y = 42color(white)("XX")rarrcolor(white)("XX")y=-2$ #

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