It went from 10 to -2, so you need to find the difference. The way you'd do this is: 10 - (-2). Do you know how to subtract a negative number from a positive number?
The lowest terms for 19/31 would be 1
A=567 km+900 km
a=1,467 km
b=567 km+169 km
b=736 km
x^2/a^2+y^2/b^2=1
x^2/(1,467)^2+y^2/(736)^2=1
Please, see the graph in the attached graph.
Thanks.