x^2 + y^2 = 20
xy = -6
.
(-6/y)^2 + y^2 = 20
x = -6/y
.
36/y^2 + y^2 = 20
x = -6/y
.
36 + y^4 = 20y^2
x = -6/y
.
Пусть t=y^2, тогда
36 + t^2 = 20t
x = -6/y
.
36 + t^2 - 20t = 0
x = -6/y
.
D = 400 - 144 = 256
t1 = (20 + √256) / 2 = 18
t2 = (20 - √256) / 2 = 2
.
t = y^2, значит
y^2 = 18
y = +-√18
y^2 = 2
y = +-√2
.
В итоге у нас получилось 4 системы
y = √18
x = -6/√18
.
y = -√18
x = 6/√18
.
y = √2
x = -6/√2
.
y = -√2
x = 6/√2
.
Задание 2:
x^2 + y^2 = 36
-x^2 + y = 6
.
x^2 + y^2 = 36
y^2 + y = 42
.
x^2 + y^2 = 36
y^2 + y - 42 = 0
.
D = 1 + 168 = 169
y1 = (-1 + √169)/ 2 = 6
y2 = (-1 - √169)/2 = -7
.
x^2 + 6^2 = 36
y = 6
.
x = 0
y = 6
.
x^2 + (-7)^2 = 36
y = -7
пустое множество.
Ответ: (0;6), (∅; -7)
Задание 3.
1/x - 1/y = 2
1/x^2 - 1/y^2 = 16
.
Пусть t = 1/x, z = 1/y, тогда
t - z = 2
t^2 - z^2 = 16
.
t = 2 + z
(2+z)^2 - z^2 = 16
.
t = 2 + z
4 + 4z + z^2 - z^2 = 16
.
t = 2 + z
4z = 12
.
t = 5
z = 3
.
5 = 1/x
3 = 1/y
.
Ответ:
x = 1/5
y = 1/3