SOLUTION: y = x^2 x^2 + y^2 = 20 I know the answer is (±2, 4) but I don't know why. Can someone please explain this to me?

Algebra ->  Quadratic-relations-and-conic-sections -> SOLUTION: y = x^2 x^2 + y^2 = 20 I know the answer is (±2, 4) but I don't know why. Can someone please explain this to me?      Log On


   

Question 152180: y = x^2
x^2 + y^2 = 20
I know the answer is (±2, 4) but I don't know why. Can someone please explain this to me?
Answer by oscargut(2103) About Me  (Show Source):
You can put this solution on YOUR website!
y = x^2
x^2 + y^2 = 20
let use 1st eq in 2nd eq
so y+(y^2)=20
y^2+y-20=0
y+=+%28-1+%2B-+sqrt%28+1%5E2-4%2A1%2A-20+%29%29%2F%282%2A1%29+
y+=+%28-1+%2B-+9%29%2F2+
then y=4 or y=-5
if y=-5 then x is not real
if y=4 then x^2=4 then x=2 or -2
solution is (2,4) and (-2,4)