1. **State the problem:** Simplify the expression $$\frac{2+\sqrt{5}}{5-\sqrt{7}} \cdot \frac{5-\sqrt{7}}{5-\sqrt{7}}$$ and verify if it equals $$\frac{\sqrt{5}+7}{8}$$.
2. **Understand the operation:** Multiplying by $$\frac{5-\sqrt{7}}{5-\sqrt{7}}$$ is multiplying by 1, so it should not change the value but rationalize the denominator.
3. **Multiply the numerators:**
$$ (2+\sqrt{5})(5-\sqrt{7}) = 2 \cdot 5 - 2 \cdot \sqrt{7} + \sqrt{5} \cdot 5 - \sqrt{5} \cdot \sqrt{7} = 10 - 2\sqrt{7} + 5\sqrt{5} - \sqrt{35} $$
4. **Multiply the denominators:**
$$ (5-\sqrt{7})(5-\sqrt{7}) = (5)^2 - 2 \cdot 5 \cdot \sqrt{7} + (\sqrt{7})^2 = 25 - 10\sqrt{7} + 7 = 32 - 10\sqrt{7} $$
5. **Rewrite the expression:**
$$ \frac{10 - 2\sqrt{7} + 5\sqrt{5} - \sqrt{35}}{32 - 10\sqrt{7}} $$
6. **Check if this equals:**
$$ \frac{\sqrt{5} + 7}{8} $$
7. **Cross-multiply to verify equality:**
$$ (10 - 2\sqrt{7} + 5\sqrt{5} - \sqrt{35}) \cdot 8 \stackrel{?}{=} (\sqrt{5} + 7)(32 - 10\sqrt{7}) $$
8. **Left side:**
$$ 8 \times 10 = 80 $$
$$ 8 \times (-2\sqrt{7}) = -16\sqrt{7} $$
$$ 8 \times 5\sqrt{5} = 40\sqrt{5} $$
$$ 8 \times (-\sqrt{35}) = -8\sqrt{35} $$
Sum left side:
$$ 80 - 16\sqrt{7} + 40\sqrt{5} - 8\sqrt{35} $$
9. **Right side:**
Expand:
$$ (\sqrt{5} + 7)(32 - 10\sqrt{7}) = \sqrt{5} \times 32 - \sqrt{5} \times 10\sqrt{7} + 7 \times 32 - 7 \times 10\sqrt{7} $$
Calculate:
$$ 32\sqrt{5} - 10\sqrt{35} + 224 - 70\sqrt{7} $$
10. **Compare both sides:**
Left: $$80 - 16\sqrt{7} + 40\sqrt{5} - 8\sqrt{35}$$
Right: $$224 - 70\sqrt{7} + 32\sqrt{5} - 10\sqrt{35}$$
They are not equal, so the original equality does not hold.
**Final answer:** The expression $$\frac{2+\sqrt{5}}{5-\sqrt{7}} \cdot \frac{5-\sqrt{7}}{5-\sqrt{7}}$$ simplifies to $$\frac{10 - 2\sqrt{7} + 5\sqrt{5} - \sqrt{35}}{32 - 10\sqrt{7}}$$ and does NOT equal $$\frac{\sqrt{5} + 7}{8}$$.
Fraction Multiplication Db191C
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