Variables in Algebra Goals I can evaluate a variable expression. I can write variable expressions for word phrases. I can write a variable expression that models a real life situation.

Variables and Expressions Special Vocabulary: variable, constant, numerical expression, algebraic expression Variable- a letter or symbol that can be used for a value that can change. Constant – a value that does not change. Numerical expression – a mathematical phrase that contains only constants and/or operations Algebraic expression – a mathematical phrase that may contain variables, constants, and/or operations

Variables and Expressions We can replace the variables with numbers and evaluate the expression. To evaluate an expression is to find it’s value. We evaluate when we simplify to the lowest possible value after substituting the number for the variable.

Evaluate the Expression when y = 3 YOU TRY: Evaluate the Expression when y = 3 a. 4y b. c. y + 8 d. 18 - y

We have to be able to “translate” words into expressions What words indicate a particular operation? Add Subtract Sum Plus More than Increase(d) by Perimeter Deposit Gain Greater than Up (flights of stairs) Total Minus Take away Difference Reduce(d) by Decrease(d) by Withdrawal Less than Fewer (than) Loss of

We have to be able to “translate” words into expressions What words indicate a particular operation? Multiply Divide Split into __ parts Cost each Quotient One-half (÷2), Third (÷3), Quarter (÷4) Into Per Percent (out of 100) Times Product Of Twice (×2), double (×2), triple (×3), etc. Half (×½), Third (×⅓), Quarter (×¼) Area (by) Percent (of) Square (times itself 2 times) Cube (times itself 3 times) … to the power of ___ (times itself ___ times)

Variables and Expressions Let’s try an example of “translating” a phrase into an algebraic expression: Nine more than a number y Can you identify the operation? “more than” means add Answer: y + 9

Variables and Expressions Let’s try another example of “translating” a phrase into an algebraic expression: 4 less than a number n Can you identify the operation? “less than” means Subtract Answer: n – 4. Why not 4 – n????? **Expressions that contain subtracting will be the hardest for us!

Variables and Expressions Let’s try another example of “translating” a phrase into an algebraic expression: A number a divided by 12 Can you identify the operation?

Variables and Expressions This one is harder…… 5 times the quantity 4 plus a number c Can you identify the operation(s)? What does the word quantity mean? Hmm……

HOMEWORK Pg 171 2-30 EVENS