Algebra 1 / Unit 1: Expressions and Real Numbers
1.3 Variables and Expressions
Notes
A variable is a letter that stands for a number. An expression combines numbers, variables and operations, with no equal sign.
- Evaluate an expression by substituting values and simplifying: if $x = 3$, then $2x + 5 = 2(3) + 5 = 11$.
- Translate words: "5 more than a number" is $n + 5$; "twice a number" is $2n$; "6 less than a number" is $n - 6$ (order matters!).
- A term is a part separated by $+$ or $-$. The number in front of a variable is its coefficient; a number alone is a constant.
Practice
Evaluate $3a^2 - 2b$ when $a = -2$ and $b = 5$.
$3(-2)^2 - 2(5) = 3(4) - 10 = 2$.
Which expression means "7 less than twice a number $n$"?
Start with twice the number, $2n$, then take away 7.
In $4x^2 - 9x + 1$, the coefficient of $x$ is:
The term is $-9x$, so its coefficient is $-9$.
Ready for more? Take the Unit 1 test.