tolong di bantu ya yang no 4 dan 5

5)
[tex] \frac{8}{3 + 2 \sqrt{21} } \times \frac{3 - 2 \sqrt{21} }{3 - 2 \sqrt{21} } = \\ \frac{24 - 16 \sqrt{21} }{9 - 6 \sqrt{21} - 6 \sqrt{21} - 4 \times 21} \\ \frac{24 - 16 \sqrt{21} }{9 - 6 \sqrt{21} - 6 \sqrt{21} - 84} \\ = \frac{24 - 16 \sqrt{21} }{9 - 84 - 12 \sqrt{21} } = \\ \frac{12 - 8 \sqrt{21} }{ - 75 - 6 \sqrt{21} } = \\ \frac{6 - 4 \sqrt{21} }{ - 75 - 3 \sqrt{21} } [/tex]
maaf ya klo salah