Arithmetic with polynomials
There is an analogy between polynomials
and the way we write integers in base 10.
For example, the integer 253
is like the polynomial 2x2 + 5x + 3
(especially if you evaluate it when x = 10).
When you add integers,
you can arrange the digits in columns and add the columns;
when you add polynomials,
you can arrange the terms in columns and add the columns.
When you multiply integers,
you need to multiply each digit in one integer by each digit in the other;
when you multiply polynomials,
you need to multiply each term in one polynomial by each term in the other.
(In some ways, arithmetic with polynomials is easier to understand,
since there is no carrying.)
For example,
adding x + 1 and 2x + 3 to get 3x + 4
is like adding 11 and 23 to get 34:
| 1 | 1 | | x | + 1 |
| 2 | 3 | | 2x | + 3 |
| 3 | 4 | | 3x | + 4 |
Similarly,
multiplying x + 1 and 2x + 3
to get 2x2 + 5x + 3
is like multiplying 11 and 23 to get 253:
| 1 | 1 | | | x | + 1 |
| 2 | 3 | | | 2x | + 3 |
| 3 | 3 | | | 3x | + 3 |
| 2 | 2 | 0 | | 2x2 | + 2x | |
| 2 | 5 | 3 | | 2x2 | + 2x | + 3 |
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last edited on 2017 August 22.
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