Simplify the following expressions and comment on the nature (rational or irrational)…

MATHEMATICS · Multi-part · AoPS · Mathematics · Special Factorizations · Special Factorizations

Problem

Simplify the following expressions and comment on the nature (rational or irrational) of each final result. Show each step of your working. (i) (35−20)+(45−25)(3\sqrt{5} - \sqrt{20}) + (\sqrt{45} - 2\sqrt{5}) (ii) 13−5\dfrac{1}{3 - \sqrt{5}} (iii) Construct an expression that uses the number 5\sqrt{5} exactly once together with any two rational numbers so that the overall value of the expression is a rational number. Justify your answer by computation.

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