Stephanie G.

# How do I come up with a middle term for an equation like x^2+99x-3870=0 in an easy way with out trial and error?

how to simplify an ax^2+bx+c

Brenda D.

tutor
Old trick, 3870, the digits add up to 18, those two digits add to 9. The very large number is divisible by 9 and 3. Save some time by going for double and triple digit multiples of 3 for factors such as 30, 90, 99 120, 129. You will have a much longer list if you start with single digit factors for this one.
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03/24/19

## 7 Answers By Expert Tutors

By: Tutor
4.8 (148)

Math Tutoring and Test Prep

Stephanie G.

thats much easier even and more clearer thank you so much

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03/11/13 Tutor
4.8 (38)

Patient knowledgeable STEM educator/former healthcare practitioner Tutor
5.0 (67)

Experienced tutor in earth sciences and basic math to trigonometry Laura M.

tutor
If a is not 1, instead of factoring c, factor the product of a and c (a*c) to get your factor pair list. Then factor by grouping.
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05/09/19

Tutor
4.9 (1,262)

Math and chemistry tutor Charles B.

Nice!  rarely taught, unfortunately...

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03/19/13 K.J. P.

tutor
Solving that system of equations doesn't give you a less complex problem. A = 99-B substituted in to the second equation gives the second equation as (99-B)*B = -3870. Expanded and terms moved around gives you B^2 - 99*B -3870 = 0
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04/02/19

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