since (a-b)(a+b) = a^2 - b^2,
(4-sqrt(5))(4+sqrt(5) = 16-5 = 11
so, multiply top and bottom by 4+sqrt(5) to get
5(4+sqrt(5))/11 = (20 + 5sqrt(5))/11
Rationalize the denominator: 5 /4-squareroot 5
(five over four minus square root five)
Please explain
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Thank you so much!! It really helped me understand!