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The trick here is to multiply by the value 1, but express it as (5 - √5)/(5 - √5). This forms a difference of squares on the bottom, eliminating the radical:

(1 + √5) / (5 + √5)
= (1 + √5)(5 - √5) / (5 + √5)(5 - √5)
= (5 - √5 + 5√5 - 5) / (25 - 5√5 + 5√5 - 5)
= 4√5 / 20
= √5 / 5

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15y ago

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