Trig Identity D34E23
1. **State the problem:** Simplify and verify the identity:
$$\frac{\cos^2 a + \cot a}{\cos^2 a - \cot a} = \frac{\cos^2 a \tan a + 1}{\cos^2 a \tan a - 1}$$
2. **Recall important formulas and identities:**
- $\cot a = \frac{\cos a}{\sin a}$
- $\tan a = \frac{\sin a}{\cos a}$
- Pythagorean identity: $\sin^2 a + \cos^2 a = 1$
3. **Simplify the left-hand side (LHS):**
$$\frac{\cos^2 a + \cot a}{\cos^2 a - \cot a} = \frac{\cos^2 a + \frac{\cos a}{\sin a}}{\cos^2 a - \frac{\cos a}{\sin a}}$$
Multiply numerator and denominator by $\sin a$ to clear denominators:
$$= \frac{\cos^2 a \sin a + \cos a}{\cos^2 a \sin a - \cos a}$$
4. **Simplify the right-hand side (RHS):**
$$\frac{\cos^2 a \tan a + 1}{\cos^2 a \tan a - 1} = \frac{\cos^2 a \cdot \frac{\sin a}{\cos a} + 1}{\cos^2 a \cdot \frac{\sin a}{\cos a} - 1} = \frac{\cos a \sin a + 1}{\cos a \sin a - 1}$$
5. **Compare LHS and RHS:**
LHS numerator: $\cos^2 a \sin a + \cos a = \cos a (\cos a \sin a + 1)$
LHS denominator: $\cos^2 a \sin a - \cos a = \cos a (\cos a \sin a - 1)$
So LHS:
$$\frac{\cos a (\cos a \sin a + 1)}{\cos a (\cos a \sin a - 1)} = \frac{\cos a \sin a + 1}{\cos a \sin a - 1}$$
Since $\cos a \neq 0$, we can cancel $\cos a$.
This matches the RHS exactly.
6. **Conclusion:** The identity holds true.
**Final answer:**
$$\frac{\cos^2 a + \cot a}{\cos^2 a - \cot a} = \frac{\cos^2 a \tan a + 1}{\cos^2 a \tan a - 1}$$
is verified.