Looking at the expression , we can see that the first coefficient is , the second coefficient is , and the last term is .
Now multiply the first coefficient by the last term to get .
Now the question is: what two whole numbers multiply to (the previous product) and add to the second coefficient ?
To find these two numbers, we need to list all of the factors of (the previous product).
Factors of :
1,2,4
-1,-2,-4
Note: list the negative of each factor. This will allow us to find all possible combinations.
These factors pair up and multiply to .
1*4 = 4 2*2 = 4 (-1)*(-4) = 4 (-2)*(-2) = 4
Now let's add up each pair of factors to see if one pair adds to the middle coefficient :
First Number | Second Number | Sum | 1 | 4 | 1+4=5 | 2 | 2 | 2+2=4 | -1 | -4 | -1+(-4)=-5 | -2 | -2 | -2+(-2)=-4 |
From the table, we can see that there are no pairs of numbers which add to . So cannot be factored.
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Answer:
So doesn't factor at all (over the rational numbers).
So is prime.
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