Question 631477

Looking at the expression {{{r^2-2r+1}}}, we can see that the first coefficient is {{{1}}}, the second coefficient is {{{-2}}}, and the last term is {{{1}}}.



Now multiply the first coefficient {{{1}}} by the last term {{{1}}} to get {{{(1)(1)=1}}}.



Now the question is: what two whole numbers multiply to {{{1}}} (the previous product) <font size=4><b>and</b></font> add to the second coefficient {{{-2}}}?



To find these two numbers, we need to list <font size=4><b>all</b></font> of the factors of {{{1}}} (the previous product).



Factors of {{{1}}}:

1

-1



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



These factors pair up and multiply to {{{1}}}.

1*1 = 1
(-1)*(-1) = 1


Now let's add up each pair of factors to see if one pair adds to the middle coefficient {{{-2}}}:



<table border="1"><th>First Number</th><th>Second Number</th><th>Sum</th><tr><td  align="center"><font color=black>1</font></td><td  align="center"><font color=black>1</font></td><td  align="center"><font color=black>1+1=2</font></td></tr><tr><td  align="center"><font color=red>-1</font></td><td  align="center"><font color=red>-1</font></td><td  align="center"><font color=red>-1+(-1)=-2</font></td></tr></table>



From the table, we can see that the two numbers {{{-1}}} and {{{-1}}} add to {{{-2}}} (the middle coefficient).



So the two numbers {{{-1}}} and {{{-1}}} both multiply to {{{1}}} <font size=4><b>and</b></font> add to {{{-2}}}



Now replace the middle term {{{-2r}}} with {{{-r-r}}}. Remember, {{{-1}}} and {{{-1}}} add to {{{-2}}}. So this shows us that {{{-r-r=-2r}}}.



{{{r^2+highlight(-r-r)+1}}} Replace the second term {{{-2r}}} with {{{-r-r}}}.



{{{(r^2-r)+(-r+1)}}} Group the terms into two pairs.



{{{r(r-1)+(-r+1)}}} Factor out the GCF {{{r}}} from the first group.



{{{r(r-1)-1(r-1)}}} Factor out {{{1}}} 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.



{{{(r-1)(r-1)}}} Combine like terms. Or factor out the common term {{{r-1}}}





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Answer:



So {{{r^2-2r+1}}} factors to {{{(r-1)(r-1)}}}.



In other words, {{{r^2-2r+1=(r-1)(r-1)}}} for all values of 'r'


So the answer is <font color="red">choice c)</font>.



Note: you can check the answer by expanding {{{(r-1)^2}}} to get {{{r^2-2r+1}}} or by graphing the original expression and the answer (the two graphs should be identical).


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