If y varies inversely as twice x. When x = 4, y = 10. how do you find y when x = 8?

1 Answer
Sep 8, 2017

color(red)(y=5 when color(blue)(x=8)

Explanation:

If y varies inversely as twice x, then
color(white)("XXX")color(blue)y=color(magenta)c/(2color(green)x)color(white)("xxx")for some constant color(magenta)c

We are told that color(green)x=color(green)4, color(blue)y=color(blue)(10) is a solution to this relation.
so
color(white)("XXX")color(blue)10=color(magenta)c/(2 * color(green)4)

color(white)("XXX")rarr color(magenta)c=80

Therefore the relation is
color(white)("XXX")color(blue)y=color(magenta)(80)/(2color(green)x)

When color(green)x=color(green)8, we have
color(white)("XXX")color(blue)y=color(magenta)(80)/(2 * color(green)8) = 5