Question

An expression is shown below: 3pf^2 − 21p^2f + 6pf − 42p^2 Part A: Rewrite the expression by factoring out the greatest common factor. (4 points) Part B: Factor the entire expression completely. Show the steps of your work. (6 points)

Answer 1

Hey there! I'm happy to help!

PART A

Let's break down each terms in the expression to find the factors that make it up and see the greatest thing they all have in common

To break up the numbers, we keep on dividing it until there are only prime numbers left.

TERM #1

Three is a prime number, so there is no need to split it up.

3pf²= 3·p·f·f              

TERM #2

We have a negative coefficient here. First, let's ignore the negative sign and find all of the factors, which are just 7 and 3. One of them has to be negative and one has to be positive for it to be negative. It could be either way, and when comparing to other, we might want one to be negative or positive to match another part of the expression to find the greatest common factor. So, we will use the plus or minus sign ±, knowing that one must be positive and one must be negative.

-21p²2f= ±7·±3 (must be opposite operations) ·p·p·f

TERM #3

6pf= 2·3·p·f

TERM #4

Since 42 is made up of 3 prime factors (2,3,7), one of them or all three must be negative, because two negatives would make it positive. We will use the plus-minus sign again on all three because it could be just one is negative or all three are, but we don't know. We can use these later to find the greatest common factor when matching.

-42p²= ±2·±3·±7·p·p

Now, let's pull out all of our factors and see the greatest thing all four terms have in common

TERM 1: 3·p·f·f  

TERM 2: ±7·±3·p·p·f     (7 and 3 must end up opposite signs)

TERM 3: 2·3·p·f

TERM 4: ±2·±3·±7·p·p   (one or three of the coefficients will be negative)

Let's first look at the numbers they share. All of them have a three. We will rewrite Term 2 as -7·3·p·p·f afterwards because 3 must be positive to match. With term four, the 3 has to positive so not all three can be negative, so that means that either the 2 or 7 has to be negative, but in the end we they will make a -14 so it does not matter which one because.

Now, with variables. All of them have one p, so we will keep this.

Almost all had an f except the fourth, so this cannot be part of the GCF.

So, all the terms have 3p in common. Let's take the 3p out of each term and see what we have left. In term 4 we will combine our ±7 and ±2 to be -14 because one has to be negative.

TERM 1: f·f

TERM 2: -7·p·f

TERM 3: 2·f

TERM 4: -14·p

The way we will write this is we will put 3p outside parentheses and put what is left of all of our terms on the inside of the parentheses.

3p(f·f+-7·p·f+2·f-14·p)

We simplify these new terms.

3p(f²-7pf+2f-14p)

Now we combine like terms.

3p(f²-7pf-14p)

If you used the distributive property to undo the parentheses you could end up with our original expression.

PART B

Completely factoring means the equation is factored enough that you cannot factor anymore. The only things we have left to factor more are the terms inside the parentheses. Although there won't be something common between all of them, one might have pairs with one and not another, and this can still be factored out, and this can be put into (a+b)(a+c). Let's find what we have in common with the three terms in the parentheses.

TERM 1: f·f

TERM 2: -7·p·f

TERM 3: 2· -7·p (I just put 7 as negative and 2 as positive already for matching)

Term 1 and 2 have an f in common.

Terms 2 and 3 have a -7p in common.

So, we see that the f and the -7p are what can be factored out among all of the terms, so let's take it out of all of them and see what is left.

Term 1: f

Term 2: nothing left here

Term 3: 2

So, this means that all we have left is f+2. If we multiply that by f-7p we will have what was in the parentheses in our answer from Part A, and we cannot simplify this any further. This means that our parentheses from Part A= (f-7p)(f+2). This shows that (f-7p) is multiplied by (f+2)

Don't forget the GCF 3p; that's still outside the parentheses!

Therefore, the answer here is 3p(f-7p)(f+2).

Have a wonderful day! :D