What answer did you get that it marked wrong? Here are some errors you could have made:
1) Did you remember to write the 9X² first? The word "from" (like the words "than" or "into") mean to write that part of the expression backwards.
2) When you squared the (5X - 6)², did you merely square each term,or did you remember that it actually means:
(5X - 6)* (5X - 6) ?
3) Finally, did you combine all like terms? Some students do nothing wrong but don'y finish every step.
