Question

(-9-4√5)(-9+4√5) solve this question.

Answer 1

Answer:

$by \: using \: this \: formulla \: \: \: \: \: (a + b)(a - b) = a {}^{2} - b {}^{2} \\ ( - 9 - 4 \sqrt{5} )( - 9 + 4 \sqrt{5} ) \\ ( - 9) {}^{2} - (4 \sqrt{5} ) {}^{2} \\ 81 - (16 \times 5) \\ 81 - 80 = 1 \: \: \: answer$

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Answer 2

Answer:

(a-b)(a+b)= a^2-b^2

81-80=1