1. **State the problem:** Verify or simplify the expression $$\frac{1+\cos A + \sin A}{1 - \cos A + \sin A} = \cot \frac{A}{2}$$.
2. **Recall the half-angle formulas:**
$$\cot \frac{A}{2} = \frac{1 + \cos A}{\sin A}$$
3. **Rewrite the left-hand side (LHS):**
$$\frac{1 + \cos A + \sin A}{1 - \cos A + \sin A}$$
4. **Try to simplify the LHS by multiplying numerator and denominator by the conjugate of the denominator:**
Multiply numerator and denominator by $$1 - \cos A - \sin A$$:
$$\frac{(1 + \cos A + \sin A)(1 - \cos A - \sin A)}{(1 - \cos A + \sin A)(1 - \cos A - \sin A)}$$
5. **Calculate denominator:**
$$(1 - \cos A)^2 - (\sin A)^2 = 1 - 2\cos A + \cos^2 A - \sin^2 A$$
Using $$\cos^2 A - \sin^2 A = \cos 2A$$:
$$= 1 - 2\cos A + \cos 2A$$
6. **Calculate numerator:**
Expand:
$$(1)(1 - \cos A - \sin A) + \cos A (1 - \cos A - \sin A) + \sin A (1 - \cos A - \sin A)$$
Simplify stepwise:
$$1 - \cos A - \sin A + \cos A - \cos^2 A - \cos A \sin A + \sin A - \sin A \cos A - \sin^2 A$$
Combine like terms:
$$1 - \cos^2 A - \sin^2 A - 2 \cos A \sin A$$
Recall $$\cos^2 A + \sin^2 A = 1$$, so numerator becomes:
$$1 - 1 - 2 \cos A \sin A = -2 \cos A \sin A$$
7. **Rewrite denominator using double angle formula:**
$$1 - 2 \cos A + \cos 2A = 1 - 2 \cos A + (2 \cos^2 A - 1) = 2 \cos^2 A - 2 \cos A$$
Factor:
$$2 \cos A (\cos A - 1)$$
8. **So the expression is:**
$$\frac{-2 \cos A \sin A}{2 \cos A (\cos A - 1)} = \frac{- \sin A}{\cos A - 1}$$
9. **Rewrite denominator:**
$$\cos A - 1 = -(1 - \cos A)$$
So expression becomes:
$$\frac{- \sin A}{\cos A - 1} = \frac{- \sin A}{-(1 - \cos A)} = \frac{\sin A}{1 - \cos A}$$
10. **Recall the half-angle identity:**
$$\cot \frac{A}{2} = \frac{1 + \cos A}{\sin A}$$
But we have $$\frac{\sin A}{1 - \cos A}$$, which is the reciprocal of $$\tan \frac{A}{2} = \frac{\sin A}{1 + \cos A}$$.
11. **Check if the original equality holds:**
The original expression simplifies to $$\frac{\sin A}{1 - \cos A}$$, which equals $$\tan \frac{A}{2}$$, not $$\cot \frac{A}{2}$$.
**Final conclusion:**
$$\frac{1 + \cos A + \sin A}{1 - \cos A + \sin A} = \tan \frac{A}{2} \neq \cot \frac{A}{2}$$
Hence, the given equation is incorrect as stated.
Trig Expression 697070
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