Taylor Lautner Braces

Writing polynomial

In the decimal system, each digit contributes to the value of the number according to the successive powers of 10: the first digit (from right) indicates units (1, ie 10 with exponent 0), the second tens (10, ie 10 with exponent 1), the third of the hundreds (100, ie 10 with exponent 2) and so on ...
Each number can then be expressed as a combination of digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 and powers of 10.
For example, the number 234 in decimal system, consisting of 2 thousands, hundreds 2, 3 tens and four units , can be written in the form:

5734 = 5 ∙ 1000 ∙ 100 + 7 + 3 ∙ 10 ∙ 1 + 4

This writing is called polynomial form of the number 5734 (base 10).
A two-digit number unknown x and y will be written in polynomial form:
10x + y.
If the exchange with the units digit of tens, yx: x + 10y

Suppose now have a two-digit number, the sum of which is 9, ie x + y = 9. From x + y = 9 y = 9-x revenue
I will then:
10x + (9-x)
This writing is the basis for solving the problems seen today in class.