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anonymous

  • one year ago

how to factor x^2-x-20

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  1. mathstudent55
    • one year ago
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    Since the coefficient of the x^2 term is 1, you need the following type of factoring: x^2 + ax + b 1. Find two numbers that multiply to b and add to a. Let's call these numbers p and q. 2. The factoring is simply (x + p)(x + q) In your case, if you compare x^2 - x - 20 to x^2 + ax + b, you have a = -1 and b = -20. You need two numbers that multiply to -20 and add to -1. What are two numbers that multiply to -20 and add to -1?

  2. anonymous
    • one year ago
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    \[x^2-x-20\\x^2-4x+5x-20\\x(x-4)+5(x-4)\\(x-4)[x+5]\\\]

  3. mathstudent55
    • one year ago
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    @eninone You wrote: \(x^2-x-20\) \(x^2-4x+5x-20\) \(x(x-4)+5(x-4)\) \((x-4)[x+5]\) Look at your second line: \(x^2-4x+5x-20\) If you add like terms, you get: \(x^2+x-20\) That is not the original polynomial. You need -5x and + 4x, not -4x and + 5x.

  4. anonymous
    • one year ago
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    @mathstudent55 thanks, @kingban follow @mathstudent55

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