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
Alan P.
Aug 1, 2016

color(green)(x=4)

Explanation:

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

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

rArr
color(white)("XXX")c=3

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

When y=12
color(white)("XXX")12=3*x
rArr
color(white)("XXX")x=4

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