SOLUTION: 3x^2 + 8x + 5 how would i factor this ?

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Question 115652: 3x^2 + 8x + 5 how would i factor this ?
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!

Looking at 3x%5E2%2B8x%2B5 we can see that the first term is 3x%5E2 and the last term is 5 where the coefficients are 3 and 5 respectively.

Now multiply the first coefficient 3 and the last coefficient 5 to get 15. Now what two numbers multiply to 15 and add to the middle coefficient 8? Let's list all of the factors of 15:



Factors of 15:
1,3,5,15

-1,-3,-5,-15 ...List the negative factors as well. This will allow us to find all possible combinations

These factors pair up and multiply to 15
1*15
3*5
(-1)*(-15)
(-3)*(-5)

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


Now which of these pairs add to 8? Lets make a table of all of the pairs of factors we multiplied and see which two numbers add to 8

First NumberSecond NumberSum
1151+15=16
353+5=8
-1-15-1+(-15)=-16
-3-5-3+(-5)=-8



From this list we can see that 3 and 5 add up to 8 and multiply to 15


Now looking at the expression 3x%5E2%2B8x%2B5, replace 8x with 3x%2B5x (notice 3x%2B5x adds up to 8x. So it is equivalent to 8x)

3x%5E2%2Bhighlight%283x%2B5x%29%2B5


Now let's factor 3x%5E2%2B3x%2B5x%2B5 by grouping:


%283x%5E2%2B3x%29%2B%285x%2B5%29 Group like terms


3x%28x%2B1%29%2B5%28x%2B1%29 Factor out the GCF of 3x out of the first group. Factor out the GCF of 5 out of the second group


%283x%2B5%29%28x%2B1%29 Since we have a common term of x%2B1, we can combine like terms

So 3x%5E2%2B3x%2B5x%2B5 factors to %283x%2B5%29%28x%2B1%29


So this also means that 3x%5E2%2B8x%2B5 factors to %283x%2B5%29%28x%2B1%29 (since 3x%5E2%2B8x%2B5 is equivalent to 3x%5E2%2B3x%2B5x%2B5)

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Answer:

So 3x%5E2%2B8x%2B5 factors to %283x%2B5%29%28x%2B1%29