Science

Math

Humanities

... and beyond

Socratic Meta
Featured Answers

Topics

If y varies directly with x, and y = -15 when x = -5, how do you write the direct linear variation equation and then use the equation to find x when y =12?

1 Answer

Aug 1, 2016

$x = 4$ $color(green)(x=4)$

Explanation:

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

We are told that when $x = - 5$ $x=-5$ , $y = - 15$ $y=-15$ .
So
$XXX - 15 = c \cdot (- 5)$ $color(white)("XXX")-15=c*(-5)$

$\Rightarrow$ $rArr$
$XXX c = 3$ $color(white)("XXX")c=3$

Therefore the direct variation equation is
$XXX y = 3 x$ $color(white)("XXX")y=3x$

When $y = 12$ $y=12$
$XXX 12 = 3 \cdot x$ $color(white)("XXX")12=3*x$
$\Rightarrow$ $rArr$
$XXX x = 4$ $color(white)("XXX")x=4$

Related questions

See all questions in Direct Variation

Impact of this question

8678 views around the world

You can reuse this answer
Creative Commons License