SOLUTION: How do you factor the following problems step by step? 1. 9-x^2 2. 4x^2+81-36x 3. 4y^2+16y+16 4. x^-25/x+5

Question 133168: How do you factor the following problems step by step?
1. 9-x^2
2. 4x^2+81-36x
3. 4y^2+16y+16
4. x^-25/x+5
Answer by jim_thompson5910(35256) (Show Source): You can put this solution on YOUR website!
I'll do the first two to get you started

# 1

Start with the given expression

Rewrite as

Rewrite as

Now use the difference of squares. Remember, the difference of squares formula is where in this case and

Plug in and

-------------------------------------------------

Answer:

So the expression

factors to

Notice that if you foil the factored expression, you get the original expression. This verifies our answer.

Start with the given expression

Rearrange the terms

Looking at we can see that the first term is and the last term is where the coefficients are 4 and 81 respectively.

Now multiply the first coefficient 4 and the last coefficient 81 to get 324. Now what two numbers multiply to 324 and add to the middle coefficient -36? Let's list all of the factors of 324:

Factors of 324:
1,2,3,4,6,9,12,18,27,36,54,81,108,162

-1,-2,-3,-4,-6,-9,-12,-18,-27,-36,-54,-81,-108,-162 ...List the negative factors as well. This will allow us to find all possible combinations

These factors pair up and multiply to 324
1*324
2*162
3*108
4*81
6*54
9*36
12*27
18*18
(-1)*(-324)
(-2)*(-162)
(-3)*(-108)
(-4)*(-81)
(-6)*(-54)
(-9)*(-36)
(-12)*(-27)
(-18)*(-18)

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

Now which of these pairs add to -36? Lets make a table of all of the pairs of factors we multiplied and see which two numbers add to -36

First Number	Second Number	Sum
1	324	1+324=325
2	162	2+162=164
3	108	3+108=111
4	81	4+81=85
6	54	6+54=60
9	36	9+36=45
12	27	12+27=39
18	18	18+18=36
-1	-324	-1+(-324)=-325
-2	-162	-2+(-162)=-164
-3	-108	-3+(-108)=-111
-4	-81	-4+(-81)=-85
-6	-54	-6+(-54)=-60
-9	-36	-9+(-36)=-45
-12	-27	-12+(-27)=-39
-18	-18	-18+(-18)=-36

From this list we can see that -18 and -18 add up to -36 and multiply to 324

Now looking at the expression , replace with (notice adds up to . So it is equivalent to )

Now let's factor by grouping:

Group like terms

Factor out the GCF of out of the first group. Factor out the GCF of out of the second group

Since we have a common term of , we can combine like terms

So factors to

So this also means that factors to (since is equivalent to )

note: is equivalent to since the term occurs twice. So also factors to

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Answer:
So factors to

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