SOLUTION: Factor - x2 - 10x - 56

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Question 76766: Factor - x2 - 10x - 56
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
First factor out a negative 1
-1%28x%5E2%2B10x%2B56%29
Now factor the quadratic in the parenthesis:
Solved by pluggable solver: Factoring Quadratics with a leading coefficient of 1 (a=1)
In order to factor 1%2Ax%5E2%2B10%2Ax%2B56, first we need to ask ourselves: What two numbers multiply to 56 and add to 10? Lets find out by listing all of the possible factors of 56


Factors:

1,2,4,7,8,14,28,56,

-1,-2,-4,-7,-8,-14,-28,-56,List the negative factors as well. This will allow us to find all possible combinations

These factors pair up to multiply to 56.

1*56=56

2*28=56

4*14=56

7*8=56

(-1)*(-56)=56

(-2)*(-28)=56

(-4)*(-14)=56

(-7)*(-8)=56

note: remember two negative numbers multiplied together make a positive number

Now which of these pairs add to 10? Lets make a table of all of the pairs of factors we multiplied and see which two numbers add to 10

||||||||
First Number|Second Number|Sum
1|56|1+56=57
2|28|2+28=30
4|14|4+14=18
7|8|7+8=15
-1|-56|-1+(-56)=-57
-2|-28|-2+(-28)=-30
-4|-14|-4+(-14)=-18
-7|-8|-7+(-8)=-15
None of these factors add to 10. So this quadratic cannot be factored. In order to solve for x, we need to use the quadratic formula.


So the quadratic -x%5E2-10x-56 cannot be factored