Sin8X Cos8X Identity 50E657
1. **State the problem:** Prove or verify the identity $$\sin^8 x - \cos^8 x = (\sin^2 x - \cos^2 x)(1 - 2\sin^2 x \cos^2 x)$$.
2. **Recall formulas and rules:**
- Difference of powers: $$a^4 - b^4 = (a^2 - b^2)(a^2 + b^2)$$.
- Pythagorean identity: $$\sin^2 x + \cos^2 x = 1$$.
3. **Rewrite left side:**
Express $$\sin^8 x - \cos^8 x$$ as $$ (\sin^4 x)^2 - (\cos^4 x)^2 $$.
4. **Apply difference of squares:**
$$ (\sin^4 x)^2 - (\cos^4 x)^2 = (\sin^4 x - \cos^4 x)(\sin^4 x + \cos^4 x) $$.
5. **Factor $$\sin^4 x - \cos^4 x$$:**
$$ \sin^4 x - \cos^4 x = (\sin^2 x - \cos^2 x)(\sin^2 x + \cos^2 x) $$.
Using Pythagorean identity, $$\sin^2 x + \cos^2 x = 1$$, so
$$ \sin^4 x - \cos^4 x = (\sin^2 x - \cos^2 x) \cdot 1 = \sin^2 x - \cos^2 x $$.
6. **Simplify $$\sin^4 x + \cos^4 x$$:**
Rewrite as
$$ (\sin^2 x)^2 + (\cos^2 x)^2 = (\sin^2 x + \cos^2 x)^2 - 2\sin^2 x \cos^2 x = 1 - 2\sin^2 x \cos^2 x $$.
7. **Combine all:**
$$ \sin^8 x - \cos^8 x = (\sin^2 x - \cos^2 x)(1 - 2\sin^2 x \cos^2 x) $$.
**Final answer:** The identity is verified and true.