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[tex] = \frac{( \sqrt{10} - \sqrt{5} )( \sqrt{10} + \sqrt{5} )}{2 \sqrt{11} + \sqrt{19} } \times \frac{2 \sqrt{11} - \sqrt{19} }{2 \sqrt{11} - \sqrt{19} } \\ = \frac{10 - 5}{2 \sqrt{11} + \sqrt{19} } \times \frac{2 \sqrt{11} - \sqrt{19} }{2 \sqrt{11} - \sqrt{19} } \\ = \frac{10 \sqrt{11} - 5 \sqrt{19} }{44 - 19} \\ = \frac{10 \sqrt{11} - 5 \sqrt{19} }{25} \\ = \frac{2}{5} \sqrt{11} - \frac{1}{5} \sqrt{19} \\ = \frac{1}{5} (2 \sqrt{11} - \sqrt{19} )[/tex]

Jawaban C

(✓10 - ✓5) (✓10 + ✓5) = 10 - 5 = 5^-1 = 1/5
(2✓11 + ✓19)^-1 = 2✓11 - ✓19
1/5 (2✓11 - ✓19) (C)