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You should look for two numbers whose product is 40, and whose sum is 13. Experimenting a little (trying different pairs of factors for 40), you can quickly realize that this works for 8 and 5. Therefore,

x2 + 13x + 40 = (x + 8) (x + 5)

that would be 8 and 5

If you want to use the quadratic equation to solve it instead of factoring, the equation is x = (-b + or - the square root of (b2- 4ac))/2a

a in this case is 1, b is 13, and c is 40

So, plug a, b, and c into the above equation and do it once with adding and once with subtracting. There will be two x values given if you do it both times, 8 and 5.

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Q: What is the quadratic equation for x2-13x plus 40?
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