E - Writing and Evaluating Expressions Lesson

Writing and Evaluating Expressions

A variable is a letter or symbol that represents a quantity that can change. A constant is a quantity that doesn't change. An algebraic expression is a variable or combination of variables, numbers, and operations.  

Examples:

2x

• Answer: "2 times x"; 2 is the coefficient and x is the variable

3y+5

• Answer: "3 times y plus 5"; 3 is the coefficient, y is the variable, and 5 is the constant

$4h^2-3$

• Answer: "4 times h to the second power minus 3"; 4 is the coefficient, h is the variable, 2 is the exponent, and 3 is the constant

Consider the expression x² + 5y + 3x + 6.

• The variables are x and y
• There are 4 terms: x², 5y, 3x, and 6
• The terms that involve a variable are variable terms and 6 is a constant
• The numbers in front of the variables are called coefficients. The coefficient of x² is 1. The coefficient of 5y is 5. The coefficient of 3x is 3.
• The expression is the sum of all 4 terms.

When you evaluate an algebraic expression, you substitute a number for the variable and find the value.

Sometimes, it's necessary to translate words into math problems. In order to do this, you need to know what words to look for.  

Words or Action	Put together or combine   Sum	Find how much more or less   Difference	Put together groups of equal parts   Times   Product	Separate into equal groups   Quotient
Mathematical Operation	Add	Subtract	Multiply	Divide

 Examples:

• "the sum of 8 and y" translates to "8 + y"
• "4 less than x" translates to "x - 4"
• "x multiplied by 13" translates to "13x"
• "the difference of 5 and y" translates to "5 - y"
• "the quotient of 9 more than x and x" translates to "(x + 9)/x"

IMAGES CREATED BY GAVS