Question

simplify:
$(4 + 3 \sqrt{5} )(4 - \sqrt{5} ).$

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Answer 1

Step-by-step explanation:

$(4 + 3 \sqrt{5} )(4 - \sqrt{5} ) \\ = {4}^{2} + (3 \sqrt{5 } - \sqrt{5} )4 - 3 \sqrt{5} \times \sqrt{5} \\ = 16 + 2 \sqrt{5} \times 4 - 3 \times 5 \\ = 16 + 8 \sqrt{5} - 15$