I've been looking over an old exam for one of my classes, and cannot decipher the train of thought used in solving (or method used) the problem on the last page:(adsbygoogle = window.adsbygoogle || []).push({});

http://people.physics.tamu.edu/kochar/FE/FE_Fall05_1.pdf

Specifically, for the first part, what is going on...? Firstly, I have the equation that I = I_{0}cos^2(phi). So if I want the intensity doubled then I end up with cos^2(phi) = 2, which isn't possible? Clearly I am thinking about this in the entirely wrong way and could use some help, thanks in advance.

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# Intensity in a Double-Slit problem?

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