(√7 + 2√3) (√7 - 2√3)

(√7 + 2√3) (√7 - 2√3)
= √7 x √7 - 2√3 x √7 + 2 √3 x √7 - 2√3 x 2√3
= 7 - 2√21 + 2√21 - 4 x 3
= 7 - 4 x 3
= 7 - 12
= -5

(a + b) (a - b) = a² - b²

[tex]=( \sqrt{7}+2 \sqrt{3})\ ( \sqrt{7}-2 \sqrt{3}) \\ \\ =( \sqrt{7})^2 - (2 \sqrt{3})^2 \\ \\ =7-(4 \times 3) \\ \\ =7-12 \\ \\ = -5 [/tex]

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