If y=21 when x=-6, how do you find x when y=7 given that y varies inversely as x?

2 Answers
Jim G.
Jul 27, 2017

#x=-18#

Explanation:

#"the initial statement is "yprop1/x#

#"to convert to an equation multiply by k the constant"#
#"of variation"#

#rArry=kxx1/x=k/x#

#"to find k use the given condition"#

#y=21" when "x=-6#

#y=k/xrArrk=yx=21xx-6=-126#

#"equation is " color(red)(bar(ul(|color(white)(2/2)color(black)(y=-126/x)color(white)(2/2)|)))#

#"when "y=7#

#x=-126/y=-126/7=-18#

Binayaka C.
Jul 27, 2017

#x= -18#

Explanation:

#y prop 1/x or y = k*1/x or x*y = k ; k# is constant of proportionality.

# y=21 . x= -6 :. k = x* y =-6 * 21 = -126# .

So the variation equation is # x * y = -126 ; y=7, x = ? #

#:. x * 7 = -126 :. x = -126/7 = -18 #

#x= -18# [Ans]

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