Use reference angles to find the exact value. Rationalize the denominator of your answer, if needed. Select "Undefined" if applicable. \[ \tan \left(-\frac{\pi}{4}\right)= \]

Step 1 ：The tangent function has a period of π, so the tangent of an angle and the tangent of that angle plus any multiple of π are the same.

Step 2 ：Therefore, the tangent of -π/4 is the same as the tangent of -π/4 + π = π/4.

Step 3 ：The tangent of π/4 is 1, so the tangent of -π/4 is also 1.

Step 4 ：However, considering the negative sign, the tangent of -π/4 is -1.

Step 5 ：Final Answer: \(\boxed{-1}\)