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Show by proof of contradiction that root 3 - root 2 is not rational?

I know how to use PoC to show that root 2 is irrational but i'm not sure how to do root 3 - root 2, help please!!

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  • Ron W
    Lv 7
    1 decade ago
    Favorite Answer

    Suppose there are positive integers m and n such that

    √3 - √2 = m/n

    Then

    (√3 - √2)² = m²/n²

    5 - 2√6 = m²/n²

    (5n² - m²)/(2n²) = √6

    Since 5n² - m² and 2n² are integers, this implies that √6 is rational. If you have already established the irrationality of √6, you're done; otherwise, it's essentially the same approach as proving the irrationality of √2.

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