Question 30461
x^2 +y^2=20 => y^2=20-x^2

x^2-2y^2=8 => x^2 -2(20-x^2)=8 => 3x^2=48 => x^2=16 => x= 4 or x= -4

y^2=20-x^2
=>y^2=20-16 => y^2=4 => y=2 or y=-2

Correct answer is D