The product of (3+ radical 5) and (3- radical 5) is

9 - 5 = 4

Difference of the squares

a² - b² = (a - b)(a + b)
with a = 3
b = √5

(3 - √5)(3 + √5) = 3² - (√5)² = 9 - 5 = 4

(3 + r5) x (3 - r5) (where r means square root).

3x3 - 3r5 + 3r5 - r5r5
9 - 5 = 4

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