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Adding Polynomials (page 1 of 2) Sections: Adding polynomials, Subtracting polynomials Adding polynomials is just a matter of combining like terms, with some order of operations considerations thrown in. As long as you're careful with the minus signs, and don't confuse addition and multiplication, you should do fine. There are a couple formats
for adding and subtracting, and they hearken back to earlier times, when
you were adding and subtracting just plain old numbers. First, you learned
addition "horizontally", like this:
Clear the parentheses, group like terms, and simplify: (2x
+ 5y) + (3x – 2y)
Horizontal addition works fine for simple examples. But when you were adding plain old numbers, you didn't try to add 432 and 246 horizontally; instead, you would "stack" them vertically, one on top of the other, and add down:
You can do the same thing with polynomials. This is how the above simplification looks when it is done "vertically":
I'll put each variable in its own column; in this case, the first column will be the x-column, and the second column will be the y-column:
I get the same solution vertically as I got horizontally: 5x + 3y. The format you use, horizontal or vertical, is a matter of taste (unless the instructions explicitly tell you otherwise). Given a choice, you should use whichever format that you're more comfortable with. Note that, for simple additions, horizontal addition (so you don't have to rewrite the problem) is probably simplest, but, once the polynomials get complicated, vertical is probably safest (so you don't "drop", or lose, terms and minus signs). Here are some more examples:
Horizontally: (3x3
+ 3x2 – 4x + 5) + (x3 –
2x2 + x – 4)
Vertically: Copyright © Elizabeth Stapel 2006-2008 All Rights Reserved
Either way, I get the same answer: 4x3 + 1x2 – 3x + 1. Note that each column in the vertical addition contains only one degree of x: the first column is the x3 column, the second column is the x2 column, the third column is the x column, and the fourth column is the constants column. This is analogous to having a thousands column, a hundreds column, a tens column, and a ones column.
It's perfectly okay to have to add three or more polynomials at once. I'll just go slowly and do each step throroughly, and it should work out right. Horizontally: (7x2
– x – 4) + (x2 – 2x – 3) + (–2x2
+ 3x + 5)
Note the 1's in the third line. Any time you have a variable without a coefficient, there is an "understood" 1 as the coefficient. If you find it helpful to write that 1 in, then do so. Vertically:
Either way, I get the same answer: 6x2 – 2
Horizontally: (x3
+ 5x2 – 2x) + (x3 + 3x
– 6) + (–2x2 + x – 2)
When you add large numbers, there are sometimes zeroes in the numbers, such as:
The zeroes in "1002" stand for "zero hundreds" and "zero tens". They are what is called "placeholders", indicating that there are no hundreds or tens. If you didn't have those zeroes there, you'd have "12", which isn't what you mean. The zeroes keep things lined up properly. When you vertically add polynomials that skip some of the degrees of x, you need to leave gaps, so the terms line up properly. Vertically:
Either way, you get the same answer: 2x3 + 3x2 + 2x – 8 Subtracting polynomials works pretty much the same way.... Top | 1 | 2 | Return to Index Next >>
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Copyright © 2006-2008 Elizabeth Stapel | About | Terms of Use |
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