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# The tangent of the sum of two angles

- Question:
- tan(a + b) = ?

- Proof:

- Formula used:
- tan(a) = sin(a)/cos(a)
- sin(a + b) = sin(a) cos(b) + cos(a) sin(b)
- cos(a + b) = cos(a) cos(b) - sin(a) sin(b)