(3+sqrt 5)(3-sqrt 5) ?

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

Working backwards,

(3+sqrt 5)(3-sqrt 5) = [ 3^2 - (sqrt5)^2 ]
= 9 - 5
= 4

(3 + √5)(3 - √5)
= 3*3 + 3*√5 - 3*√5 - √5*√5
= 9 + 3√5 - 3√5 - √25
= 9 - 5
= 4

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

Answer: 4

(A-B)(A+B)=A^2 - B^2,
9-5=+4

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

hence your expression=3^2-5 or 4

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