Expert: Lynn Houston - 11/1/2011

Question
I need to know how to do variable expressions. My teacher it trying to teach me but I just don't get it really! I'm having the most trouble in knowing when you are suppose yo add or subtract. The only thing I know is combine like terms and bring the sign with it! If you could help me that would be great! The problem looks like this.          (9x-8xsquare-12plus7xthirdpower)plus(-3xthirdpower-7xsecondpower plus5x-9)

Answer
9x-8x^2-12 + 7x^3 + (-3x^3-7x^2+5x-9) If this is the correct problem, then here is how you solve it.

since the items in the parens are added, they retain their original sign, so you can just remove the plus sign and the parens

9x - 8x^2 - 12 + 7x^3 - 3x^3 - 7x^2 + 5x - 9  So, start with the variable with the highest exponent

maybe using brackets will help you process what needs to be done


(7x^3 - 3x^3) + (- 8x^2 - 7x^2) + (9x + 5x) + (-12 - 9)    
(4x^3) + (- 15x^2 + (14x) + (-21)   no remove the brackets
4x^3 - 15x^2 + 14x - 21

hope this helps