math

Y is directly proportional to the square of x.
Find the percentage increase in value of y when x is doubled

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  1. Y=kx^2
    When x is doubled
    Y=(2x)^2
    Therefore Y=4x^2

    Percentage increase=(3kx^2)/kx^2 ×100%
    =300%
    Is it good?

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  2. correct, except I would keep the k in the calculation

    old y = k x^2
    new y = k (4x^2)
    change in y = 3k x^2
    percentage change = 3k x^2/(k x^2) = 3
    or 300%

    e.g. enter 1 and 4 for the following applet,
    http://www.marshu.com/articles/calculate-percentage-increase-decrease-percent-calculator.php

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