Question 152180
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 = (-1 +- sqrt( 1^2-4*1*-20 ))/(2*1) }}} 
{{{y = (-1 +- 9)/2 }}} 
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)