They are sufficient together.
slope = b-0/a-0
since slope is negative that means either b OR a is negative. ONLY one of them can be negative. according to statement 2 a is less than be therefore a is negative therefor b is positive.
Just noticed the excel file had more than one question. I answered the first. Open new threads for the others. It's much easier that way and it helps others too. Be nice if you could type it too.
Is this (red) not an assumpion?
a<b can mean,
a = 2, b = 4; a = -5, b = -2 ?
OR am I missing somthing
statement 1 says that the slope is negative therefor one and only of of them can be negative. if we have (2,4) or (-5,-2) as you pointed out the slope will be positive. To have a negative slope on of the coordinates has to be negative. Hope that helps.