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math problem

posted by on .

please help

Simplify

Multiply

(2ã7-4ã2)(5ã7+10ã2)

  • math problem - ,

    Assuming your garbled symbol means √, we have

    (2√7 - 4√2)(5√7 + 10√2)
    just think of these as polynomials in x and y

    (2x-4y)(5x+10y) = 10x^2 - 40y^2

    letting x = √7 and y = √2, we have

    10(√7)^2 - 40(√2)^2 = 10*7-40*2 = -10

    Some work could have been saved by noting that

    (2√7 - 4√2)(5√7 + 10√2)
    = 2(√7-2√2) * 5(√7+√2)
    = 10(√7-2√2)(√7+2√2)
    = 10(7-8)

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