If y varies directly as the square of x. When x = 2, y = 20, how do you find y when x = 4?

1 Answer
Apr 5, 2017

#y=80#

Explanation:

Note - #color(blue)"the square of x is expressed as " x^2#

#rArrypropx^2#

Make into an equation by introducing k, the constant of variation.

#rArry=kxxx^2=kx^2#

To find k, use the condition given x = 2 when y = 20

#y=kx^2rArrk=y/x^2=20/4=5#

#"Thus " color(red)(bar(ul(|color(white)(2/2)color(black)(y=5x^2)color(white)(2/2)|)))#

#x=4toy=5xx4^2=80#