Does anyone know how to do this math

x^2 + 81y^2 = 8100
9y + x + 90= 0


(x, y) = ( )
(x, y) = ( )

x^2 + 81y^2 = 8100 ......(1)

9y + x + 90 = 0
x = - 9y - 90 .......(2)

Put x = - 9y - 90 into (1);
( - 9y - 90)^2 + 81y^2 = 8100
81y^2 + 1620y + 8100 + 81y^2 = 8100
162y^2 + 1620y + 8100 - 8100 = 0
162y^2 + 1620y = 0
162y(y + 10) = 0
162y = 0 or y + 10 = 0
y = 0 or y = - 10

Put y = 0 into (2);
x = - 9y - 90
x = - 9(0) - 90
x = 0 - 90
x = - 90 ...(- 90; 0)

Put y = - 10 into (2);
x = - 9y - 90
x = - 9(- 10) - 90
x = 90 - 90
x = 0 ...(0; - 10)

Therefore, (x,y) = (- 90; 0) and (0; - 10) ...ANSWERS!!

(1) given x^2+81y^2=81 solñ; x^2+(9y)^2=90^2 =>x+9y=90, so simplifying and factorizing x=-90 and y=0 that is(x,y)=(-90,0)
(2)-given x+9y=90...1 x=>90-9y...2 puting 2 in 1,y=0 substituting y=0 in 1 x=90. That is (x,y)=(90,0)

using the second equation
x=-9y-90

plug that into the first equation
(-9y-90)^2+81y^2=8100
81y^2+1620y+8100+81y^2=8100
162y^2+1620y=0
y=0

x=-9(0)-90
x=-90

(-90,0)

yes

yes, i do.