# How to solve for $x \times x = y$ when I know $y$?

I'm trying to figure out a problem for a program I'm writing. I am calculating color values, and they get premultiplied by the alpha. I want to figure out what the alpha was before hand and divide the color by that.

I have the new premultiplied alpha (let's say alpha is $.25$ or $25\%$)

$\alpha = .25 * .25$;

$\alpha = .0625$

Given this information, I want to figure out $.25$ from $.0625$

$.0625 = x \times x$

My math is super bad/rusty. Any help would be great!

• Do you know what a square root is?... – Cure Jun 22 '14 at 2:48
• Ah, easy. Thanks. – M2tM Jun 22 '14 at 2:49