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We have learned that, in an algebraic expression, letters can stand for numbers. Here are the steps for evaluating an expression:
However, since variables "vary", the value assigned to a particular variable can change from problem to problem, just not within a single problem.
Here's an example. Let's evaluate the expression 2x^{3} – x^{2} + y for x = 3 and y = –2.
Evaluate: 
Make sure the equation is clear and you know which variable is which. It's a good idea to write the expression down and what each variable is. Leave yourself enough room to work out the problem line by line, with each step right below the previous one. 
2(3)^{3}
– (3)^{2} + (2)

Replace each variable in the expression with its value. In this example, this means each x becomes a 3 and each y becomes a 2. It's a good idea to use parentheses to keep track of this. Tip: Be extra careful with negative numbers! 
2(27)
 9 + (2)

Perform operations with exponents. 
54
 9 +(2)

Perform operations with multiplication and division. 
43

Perform operations with addition and subtraction 
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