Answer :
y^2 - (y+5)^2 = 20
starting with (y+5)^2 that's y^2 + 5y + 5y + 25
then you change the signs and get
y^2 - y^2 - 10y - 25 = 20
so -10y = 45 >> 10y = -45 >> y = -4,5
answer: A
starting with (y+5)^2 that's y^2 + 5y + 5y + 25
then you change the signs and get
y^2 - y^2 - 10y - 25 = 20
so -10y = 45 >> 10y = -45 >> y = -4,5
answer: A