Question 316984


Looking at {{{3x^2-10xy+8y^2}}} we can see that the first term is {{{3x^2}}} and the last term is {{{8y^2}}} where the coefficients are 3 and 8 respectively.


Now multiply the first coefficient 3 and the last coefficient 8 to get 24. Now what two numbers multiply to 24 and add to the  middle coefficient -10? Let's list all of the factors of 24:




Factors of 24:

1,2,3,4,6,8,12,24


-1,-2,-3,-4,-6,-8,-12,-24 ...List the negative factors as well. This will allow us to find all possible combinations


These factors pair up and multiply to 24

1*24

2*12

3*8

4*6

(-1)*(-24)

(-2)*(-12)

(-3)*(-8)

(-4)*(-6)


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



Now which of these pairs add to -10? Lets make a table of all of the pairs of factors we multiplied and see which two numbers add to -10


<table border="1"><th>First Number</th><th>Second Number</th><th>Sum</th><tr><td align="center">1</td><td align="center">24</td><td>1+24=25</td></tr><tr><td align="center">2</td><td align="center">12</td><td>2+12=14</td></tr><tr><td align="center">3</td><td align="center">8</td><td>3+8=11</td></tr><tr><td align="center">4</td><td align="center">6</td><td>4+6=10</td></tr><tr><td align="center">-1</td><td align="center">-24</td><td>-1+(-24)=-25</td></tr><tr><td align="center">-2</td><td align="center">-12</td><td>-2+(-12)=-14</td></tr><tr><td align="center">-3</td><td align="center">-8</td><td>-3+(-8)=-11</td></tr><tr><td align="center">-4</td><td align="center">-6</td><td>-4+(-6)=-10</td></tr></table>



From this list we can see that -4 and -6 add up to -10 and multiply to 24



Now looking at the expression {{{3x^2-10xy+8y^2}}}, replace {{{-10xy}}} with {{{-4xy+-6xy}}} (notice {{{-4xy+-6xy}}} adds up to {{{-10xy}}}. So it is equivalent to {{{-10xy}}})


{{{3x^2+highlight(-4xy+-6xy)+8y^2}}}



Now let's factor {{{3x^2-4xy-6xy+8y^2}}} by grouping:



{{{(3x^2-4xy)+(-6xy+8y^2)}}} Group like terms



{{{x(3x-4y)-2y(3x-4y)}}} Factor out the GCF of {{{x}}} out of the first group. Factor out the GCF of {{{-2y}}} out of the second group



{{{(x-2y)(3x-4y)}}} Since we have a common term of {{{3x-4y}}}, we can combine like terms


So {{{3x^2-4xy-6xy+8y^2}}} factors to {{{(x-2y)(3x-4y)}}}



So this also means that {{{3x^2-10xy+8y^2}}} factors to {{{(x-2y)(3x-4y)}}} (since {{{3x^2-10xy+8y^2}}} is equivalent to {{{3x^2-4xy-6xy+8y^2}}})




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     Answer:

So {{{3x^2-10xy+8y^2}}} factors to {{{(x-2y)(3x-4y)}}}