Evaluate: `int_0^(pi//4)tan^3x\ dx`

Explanation

To evaluate the integral \( I = \int_0^{\frac{\pi}{4}} \tan^3 x \, dx \), we can use the identity for \( \tan^2 x \) and rewrite the integral as follows:

### Step 1: Rewrite the integral
We can express \( \tan^3 x \) as \( \tan^2 x \cdot \tan x \):
\[ I = \int_0^{\frac{\pi}{4}} \tan^2 x \cdot \tan x \, dx \]

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