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

1 Answer
Alan P.
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#

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