Questions on Algebra: Distributive, associative, commutative properties, FOIL answered by real tutors!

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Question 151213This question is from textbook Intermediate Algebra
: I need help!!! I am suppose to describe a strategy for factoring a polynomial and give example showing all your steps. Can someone help me on this one.This question is from textbook Intermediate Algebra
: I need help!!! I am suppose to describe a strategy for factoring a polynomial and give example showing all your steps. Can someone help me on this one.
Answer by jim_thompson5910(9404) About Me  (Show Source):
You can put this solution on YOUR website!

Let's say that we want to factor 4x^2-14x-30


4x^2-14x-30 Start with the given expression.


2(2x^2-7x-15) Factor out the GCF 2



Now let's focus on the inner expression 2x^2-7x-15


Looking at the expression 2x^2-7x-15, we can see that the first coefficient is 2, the second coefficient is -7, and the last term is -15.


Now multiply the first coefficient 2 by the last term -15 to get (2)(-15)=-30.


Now the question is: what two whole numbers multiply to -30 (the previous product) and add to the second coefficient -7?


To find these two numbers, we need to list all of the factors of -30 (the previous product).


Factors of -30:
1,2,3,5,6,10,15,30
-1,-2,-3,-5,-6,-10,-15,-30


Note: list the negative of each factor. This will allow us to find all possible combinations.


These factors pair up and multiply to -30.
1*(-30)
2*(-15)
3*(-10)
5*(-6)
(-1)*(30)
(-2)*(15)
(-3)*(10)
(-5)*(6)

Now let's add up each pair of factors to see if one pair adds to the middle coefficient -7:


First NumberSecond NumberSum
1-301+(-30)=-29
2-152+(-15)=-13
3-103+(-10)=-7
5-65+(-6)=-1
-130-1+30=29
-215-2+15=13
-310-3+10=7
-56-5+6=1



From the table, we can see that the two numbers 3 and -10 add to -7 (the middle coefficient).


So the two numbers 3 and -10 both multiply to -30 and add to -7


Now replace the middle term -7x with 3x-10x. Remember, 3 and -10 add to -7. So this shows us that 3x-10x=-7x.


2x^2+highlight(3x-10x)-15 Replace the second term -7x with 3x-10x.


(2x^2+3x)+(-10x-15) Group the terms into two pairs.


x(2x+3)+(-10x-15) Factor out the GCF x from the first group.


x(2x+3)-5(2x+3) Factor out 5 from the second group. The goal of this step is to make the terms in the second parenthesis equal to the terms in the first parenthesis.


(x-5)(2x+3) Combine like terms. Or factor out the common term 2x+3


So 2(2x^2-7x-15) factors down to 2(x-5)(2x+3)


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Answer:


So 4x^2-14x-30 factors to 2(x-5)(2x+3).