Answer:
1) = 2
2) =- -5 as workings show -20/4 = -5/1 = -5
3) = undefined we show equation x = 8
4) = 2/7
5) = undefined we show equation as y=6
6) = undefined as workings show 12/3 = 4/3 positive
7) = 12 as workings show 24/2 = 12/1
We use the formula y2-y1 / x2-x1
As we enter a value say - 4 up on y1
or - 4 up on x1
Then it becomes - - (two subtractions together) they become plus = positive + and either one has a negative sign in front.
if used as second order in bold in formula.