Factor Completely
x^2 – 5x – 84
2007-10-23 15:53:45 · 5 answers · asked by sumguy 1 in Science & Mathematics ➔ Mathematics
Answer:
(x-12)(x+7)
See the section on "General Quadratics" in the following tutorial:
http://faculty.ed.umuc.edu/~swalsh/Math%20Articles/Factoring.html
Quick summary of key to this problem:
What are ways to factor -84 such that the sum of the two factors is -5:
1 and -84, no good
4 and -21, no good
7 and -12, bingo!
2007-10-23 16:02:50 · answer #1 · answered by Ryan 3 · 0⤊ 0⤋
We want factors of 84. Since the 84 is negative, we need to subtract the two factors to get the coefficient of x, i.e. we need factors of 84 that subtract to 5. The ones that do the trick are 7 and 12. Since we want -5x rather than +5x, we go with +7 and -12 to get
x^2 - 5x - 84 = (x-12) (x+7).
2007-10-23 15:58:42 · answer #2 · answered by Scarlet Manuka 7 · 0⤊ 0⤋
You need two number A and B that the product AB is -84, and the sum A + B = -5. Two numbers that would work here are -12 and 7, so the factor would be:
(x + A)(x + B) = (x + 7)(x - 12).
Always check this!
(x + 7)(x - 12) = x^2 - 12x + 7x - 84,
so that works.
2007-10-23 15:58:50 · answer #3 · answered by mathmo 1 · 0⤊ 0⤋
x^2 – 5x – 84
(x +7) (x-12)
2007-10-23 15:59:13 · answer #4 · answered by ptolemy862000 4 · 0⤊ 0⤋
you factor it into
(x-12)(x+7)
heres a web that can teach you the steps
http://mathforum.org/dr.math/faq/faq.learn.factor.html
2007-10-23 16:01:35 · answer #5 · answered by Myth 2 · 0⤊ 0⤋