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anonymous

  • 5 years ago

There are some binomials that can be expanded directly by a general inspection. For example (x+a)(x+b)=x^2+x(a+b)+ab. Can you help me to recognize to which case does the following expression belongs to? (3x+7)(7x-3)

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  1. anonymous
    • 5 years ago
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    I found the answer guys :)

  2. radar
    • 5 years ago
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    Did you expand it by inspection? Or did you use paper & pencil?

  3. anonymous
    • 5 years ago
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    after a while, FOILing with small numbers becomes easy in the example above, you would do I'm not sure where i learned this from, or maybe i came up with it (i'm definitely not the first to do so!) (ax + b)(cx + d) (a*b)x^2 + (bc + ad)x + bd it's really just a "formula" for FOIL so your example (3x+7)(7x-3) (3 * 7)x^2 + (49 + -9)x + -21 21x^2 + 40x - 21

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