1) You can indicate an exponent with this guy: "^". "X-squared" or "x to the second power" would be simply "x^2". Make sure you separate with space and parentheses to clarify meaning.
2) You are in Pre-Algebra, so this is a little harder to explain, but not too bad. The idea is simply, if you multiply two things and get zero ONE OF the two things MUST be zero. It can be EITHER or BOTH.
In your first example:
Substituting a = -1 gives (2(-1)-2)((-1)+1) = (-2-2)(-1+1) = (-4)(0) = 0 -- So you are right!!
Substituting a = +1 gives (2(1)-2)((1)+1) = (2-2)(1+1) = (0)(2) = 0 -- So you are wrong!!
You must consider BOTH factors. You seem to be grabbing only one.
Let's try that last one.
8y^2 + 6y - 9 = 0
Do we get to factor it? I hope so.
(4y-3)(2y+3) = 0
From this factor, 2y+3, we get y = -3/2. You were close, but seem to have missed a sign.
From this factor, 4y-3, we get y = 3/4. You didn't mention this one.
So, to sum up...
1) Be sure to get BOTH possible answers. One won't do when there are two available.
2) Generally, one should not convert things to decimals. You will find, one day, trust me on this, that fluency in fractions will be to your advantage.
