If Y varies inversely with the square of x. When x is 5, y is 4/5, how do you find value of y, when x equals 8?

1 Answer
SCooke
Apr 22, 2016

Set up the described equation, solve it for the proportionality constant, and then use your completed equation to calculate the new value.

Explanation:

First, set up the described equation.
#y = a * 1/(x)^2#
Then, given x = 5 and y = 4/5 we can solve for the proportionality constant of the equation.
# 4/5 = a * 1/(5)^2 ; a = 4/5 * (5)^2 ; a = 4/5 *25 = 20#
SO, our equation is #y = 20/(x)^2#

#when x = 8, y = 20/(8)^2# ; y = 20/64 = 0.3125

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