Billy found the slope of the line through the points (2,5) and (-2,-5) using the equation
2- (-2)
5- (-5) = 2/5. what mistake did he make

Slope is calculated as the change in y over the change in x so you would need to do 5- (-5) which turns the negative sign to a positive making it 5+5=10 and the same thing with the 2s 2-(-2)=4 so the answer would be 10/4 or 5/2. Billy did the reciprocal.

Here are the answers to the ones that i could see.