Question

Please help me with this question

Answer 1

1. y^2 - (y^2 + 10y+ 25) = 20
2. -10y -25 = 20
3. -10y = 45
4. y = -4.5

Answer 2

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