If y is directly proportional to the square of x, when x=4 y = 25, how do you find an expression for y in terms of x?

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Answer 1 · 2015-07-18T01:01:32

Find the quadratic expression.

y would be in the form: $y = a x^{2}$ $y = ax^2$

$25 = a {(4)}^{2}$ $25 = a(4)^2$ --> 25 = 16a --> $a = \frac{25}{16}$ $a = 25/16$

The expression would be: $y = \frac{25 x^{2}}{16}$ $y = (25x^2)/16$

Check: x = 4 --> y = 25

Answer 2 · 2015-07-18T01:07:36

$y = 1.562 x^{2}$ $y=1.562x^2$

$y \propto x^{2}$ $ypropx^2$

So:

$y = k x^{2}$ $y=kx^2$

So:

$25 = k \times 4^{2}$ $25=kxx4^2$

$k = \frac{25}{16} = 1.562$ $k=25/16=1.562$

So:

$y = 1.562 x^{2}$ $y=1.562x^2$