Question 81770: How do I subtract and solve 2x – 3x2 + 5x3 from 5x3 + 4x – x2?
Answer by bucky(2189)   (Show Source):
You can put this solution on YOUR website! Write down the "from" expression first and arrange its terms in descending powers of x
(x-cubed term first, x-squared term next, and x-term last). When you do you get:
.
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Do the same thing to the "take away" term, and write it under the "from" expression
to get:
.
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Next, change the signs of each term in the bottom row:
.
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On your paper, you can draw a line under the bottom expression, just as you would for
an ordinary subtraction problem involving numbers.
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Now all you have to do is add the like terms in the vertical columns. Seems odd that you
add, but by changing the signs of the terms in the bottom expression, you have converted
the problem from a subtraction problem to an addition problem.
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In the first vertical column you add  and note that they cancel out.
If you want, you can write a zero at the bottom of this column, or you can just leave it
blank.
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In the next vertical column you add  and the result is  .
You can write this term at the bottom of this vertical column.
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Finally, in the last column you add  and you get  . Write this at
bottom of the third vertical problem.
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Putting your answers together you should see the following terms in the bottom row:
.
 and you just drop the zero to make the answer 
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With more practice you will be able to work problems such as these without writing
things in columns, but first you need to practice the pattern of subtraction and arranging
things in columns is a good way to start.
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Hope this helps.
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