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I'm particle physics at the moment and I don't get why the average value of cosˆ2 is 1/3.

The section :

**<< Mentor Note -- Thread moved from the technical forums so no Homework Help Template is shown >>**I'm particle physics at the moment and I don't get why the average value of cosˆ2 is 1/3.

The section :

**My solution is :**

[tex]< cos^{2}(\alpha)> = \frac{1}{\pi - 0} \int_{0}^{\pi } cos^{2}(\alpha)sin(\alpha)d\alpha[/tex]

I substitute

[tex]u = cos(\alpha)[/tex]

so i get

[tex]-\frac{1}{\pi}\int_{1}^{-1}u^{2}du = \frac{2}{3\pi}[/tex]

What im i doing wrong ? :(

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