Expert: Wei Chong - 6/19/2008

Question
(-1x)(x-9)

Answer
Hi Ernesto,

To remove the brackets, first you have to understand the basics behind removing brackets. If you not so sure about it, the following link contains a lesson on it (scroll down the page to watch the math video):

http://www.mathexpression.com/simplifying-algebraic-expressions.html

With the basics in mind, let's solve your question step-by-step:

1) After going through the removing brackets lesson about, we should know that we can remove the terms by multiplying all the terms in the brackets with the term outside the brackets.

In summary, if we are asked to remove the brackets in A(B-C), we should get:
         
  A(B - C) = AB - AC


2) So now, using A(B - C) = AB - AC as a guide, we get:

  (-1x)(x - 9) = (-1x)*(x) - (-1x)*(9) <-- we need to simplify this
               = -1x^2 -(-9x)  <-- '-' multiply by '-' gives '+'
               = -1x^2 + 9x   <-- -1x^2 can be written as -x^2
               = -x^2 + 9x   <--here's the answer.


Best Regards,
Wei Chong