Question

Помогите решить систему: $\left \{ {{x ^{2}+y ^{2}=20 } \atop {2y-x=0}} \right.$

Answer 1

x^2 + y^2 = 20
2y - x = 0
====
(2y)^2 + y^2 = 20
x = 2y
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4y^2 +y^2 = 20
x = 2y
====
5y^2 = 20
x = 2y
====
y^2 = 4
x = 2y
====
y_1 = 2
x_1 = 2*2
====
y_2 = -2
x_2 = 2*(-2)
====
y_1 = 2
x_1 = 4
====
y_2 = -2
x_2 = -4 
Ответ: (4;2) U (-4;-2)