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# B1.02: Section 1

Use the distributive property and other properties to simplify expressions and check your work.

### Distributive Property:

For any real numbers a, b, and c:     a(b + c) = ab + ac. For any real numbers a, b, and c:     a(bc) = abac
The fact that two expressions are equal means that they are equal for any values of the variable. So you can check by taking a few values for the variable and making sure that those do make the two sides equal. Usually we don’t use the values 0 or 1 or 2 as the value for the variable and it is best to avoid numbers that already appear in the problem.

### Example 1

Simplify $10(4x+5)$.

 Solution: $10(4x+5)=40x+50$ Partial Check:   Use \begin{align}&\,\,\,\,\,\,10(4x+5)=40x+50\\&10(4\cdot3+5)\,\,?=?\,40\cdot3+50\\&\,10(12+5)\,\,\,?=?\,\,120+50\\&\,\,\,\,\,\,\,10(17)\,\,\,?=?\,\,170\\&\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,170\,\,\,\,=\,\,\,\,170\\\end{align}

### Example 2

Simplify $-6(x+9)$.

 Solution: $-6(x+9)=-6x-54$ Partial Check: Use $x=5$ \begin{align}&\,\,\,\,-6(x+9)=-6x-54\\&-6(5+9)\,\,\,?=?\,\,\,-6*5-54\\&\,\,\,-6(14)\,\,\,?=?\,\,\,-30-54\\&\,\,\,\,\,\,\,\,\,\,\,\,\,-84\,\,=\,\,-84\\\end{align}

### Example 3

Simplify $2(3x-7)$.

 Solution: \begin{align}&2(3x-7)=2\cdot3x-2\cdot7\\&\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,=6x-14\\\end{align} Partial Check: Use $x=5$ \begin{align}&2(3\cdot5-7)\,\,\,\,\,?=?\,\,\,\,6\cdot5-14\\&\,\,2(15-7)\,\,\,\,?=?\,\,\,30-14\\&\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,2(8)\,\,\,=\,\,\,16\\\end{align}

### Example 4

Simplify $17-5(4x-12)$.

 Solution: \begin{align}&17-5(4x-12)=17-20x-(-60)\\&\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,=17-20x+60\\&\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,=77-20x\\\end{align} Partial Check: Use $x=3$ \begin{align}&17-5(4\cdot3-12)\,\,\,?=?\,\,\,77-20\cdot3\\&\,\,\,17-5(12-12)\,\,\,?=?\,\,77-60\\&\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,17-0\,\,\,=\,\,\,\,17\\\end{align}