Alissa Fong

**MA, Stanford University**

Teaching in the San Francisco Bay Area

Alissa is currently a teacher in the San Francisco Bay Area and Brightstorm users love her clear, concise explanations of tough concepts

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Evaluating an expression means to find the value of that expression by plugging in specific values for the variables. Keep in mind a few things when evaluating expressions with exponents. When substituting the value in for the variable raised to an exponent, remember to put parenthesis around the value to help you remember that the exponent is raising the entire value, including any negative signs. So if you are substituting in -2 for the value of x in the expression x^2, then it should be written as (-2)^2. This means that -2 is being squared. This is different from -2^2, which means that 2 is being squared, then multiplied by a negative.

Evaluate x² take away y to the third power when x equals 4 and y equals 2. You could also read this as x² take away y cubed. To the third power we can also say is cubed.

In order to evaluate this which just means plugging stuff and simplify what I’m going to do is rewrite this problem using those numbers instead of x, I’m going to rewrite it using the number -4 being really careful with parentheses because I want the whole base -4 to be squared. I'm going to subtract from that my value for the y which is 2 to the third power.

Once you have those numbers substituted in there and you've been careful with your parenthesis these problems can be pretty easy. -4 times itself is +16 and then this is 2 times 2 times 2 again, well 2 times 2 is 4 times 2 again is 8 so what I’m dealing with is 16 take away 8 which is just equal to 8.

When you are asked to evaluate an exponential expression meaning a problem like this that has exponents involved, all I think you guys need to do in order to be successful is remember to use parentheses especially if there is a negative base involved.