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How do you write the direct variation equation if y=42 as x=6, find y for the x-value 3?

1 Answer

Oct 9, 2015

$y = 7 x$ $y=7x$
when $x = 3$ $x=3$ then $y = 21$ $y=21$

Explanation:

If $y$ $y$ varies directly as $x$ $x$
$XX y = c \cdot x$ $color(white)("XX")color(red)(y)=c*color(blue)(x)$ for some constant $c$ $c$

We are told
$XX 42 = c \cdot 6$ $color(white)("XX")color(red)(42) = c*color(blue)(6)$
$\Rightarrow XX c = 7$ $rArrcolor(white)("XX")c=7$

So the equation is
$XX y = 7 x$ $color(white)("XX")y=7x$

When $x = 3$ $x=3$
$XX y = 7 (3) = 21$ $color(white)("XX")y=7(3) = 21$

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