7)
A
number in the form of x2 + xy + y2 can have several
different x and y solutions.
(x, y) = (y,
x) = (-x, -y) = (-y, -x) = (x, -x – y) = (-x – y, x) = (-x, x + y) = (x + y,
-x) = (-x – y, y) = (y, -x – y) = (x + y, -y) = (-y, x + y). For example, if x = 2 and y = 3, then x2
+ xy + y2 = 22 + 2∙3 + 32 = 19, so (2, 3) =
19. Since -x – y = -5 and x + y = 5, 19
can also be obtained by (3, 2), (-2, -3), (-3, -2), (2, -5), (-5, 2), (-2, 5),
(5, -2), (-5, 3), (3, -5), (5, -3) and (-3, 5).
-10
|
-9
|
-8
|
-7
|
-6
|
-5
|
-4
|
-3
|
-2
|
-1
|
0
|
1
|
2
|
3
|
4
|
5
|
6
|
7
|
8
|
9
|
10
|
||
10
|
100
|
91
|
84
|
79
|
76
|
75
|
76
|
79
|
84
|
91
|
100
|
111
|
124
|
139
|
156
|
175
|
196
|
219
|
244
|
271
|
300
|
10
|
9
|
91
|
81
|
73
|
67
|
63
|
61
|
61
|
63
|
67
|
73
|
81
|
91
|
103
|
117
|
133
|
151
|
171
|
193
|
217
|
243
|
271
|
9
|
8
|
84
|
73
|
64
|
57
|
52
|
49
|
48
|
49
|
52
|
57
|
64
|
73
|
84
|
97
|
112
|
129
|
148
|
169
|
192
|
217
|
244
|
8
|
7
|
79
|
67
|
57
|
49
|
43
|
39
|
37
|
37
|
39
|
43
|
49
|
57
|
67
|
79
|
93
|
109
|
127
|
147
|
169
|
193
|
219
|
7
|
6
|
76
|
63
|
52
|
43
|
36
|
31
|
28
|
27
|
28
|
31
|
36
|
43
|
52
|
63
|
76
|
91
|
108
|
127
|
148
|
171
|
196
|
6
|
5
|
75
|
61
|
49
|
39
|
31
|
25
|
21
|
19
|
19
|
21
|
25
|
31
|
39
|
49
|
61
|
75
|
91
|
109
|
129
|
151
|
175
|
5
|
4
|
76
|
61
|
48
|
37
|
28
|
21
|
16
|
13
|
12
|
13
|
16
|
21
|
28
|
37
|
48
|
61
|
76
|
93
|
112
|
133
|
156
|
4
|
3
|
79
|
63
|
49
|
37
|
27
|
19
|
13
|
9
|
7
|
7
|
9
|
13
|
19
|
27
|
37
|
49
|
63
|
79
|
97
|
117
|
139
|
3
|
2
|
84
|
67
|
52
|
39
|
28
|
19
|
12
|
7
|
4
|
3
|
4
|
7
|
12
|
19
|
28
|
39
|
52
|
67
|
84
|
103
|
124
|
2
|
1
|
91
|
73
|
57
|
43
|
31
|
21
|
13
|
7
|
3
|
1
|
1
|
3
|
7
|
13
|
21
|
31
|
43
|
57
|
73
|
91
|
111
|
1
|
0
|
100
|
81
|
64
|
49
|
36
|
25
|
16
|
9
|
4
|
1
|
0
|
1
|
4
|
9
|
16
|
25
|
36
|
49
|
64
|
81
|
100
|
0
|
-1
|
111
|
91
|
73
|
57
|
43
|
31
|
21
|
13
|
7
|
3
|
1
|
1
|
3
|
7
|
13
|
21
|
31
|
43
|
57
|
73
|
91
|
-1
|
-2
|
124
|
103
|
84
|
67
|
52
|
39
|
28
|
19
|
12
|
7
|
4
|
3
|
4
|
7
|
12
|
19
|
28
|
39
|
52
|
67
|
84
|
-2
|
-3
|
139
|
117
|
97
|
79
|
63
|
49
|
37
|
27
|
19
|
13
|
9
|
7
|
7
|
9
|
13
|
19
|
27
|
37
|
49
|
63
|
79
|
-3
|
-4
|
156
|
133
|
112
|
93
|
76
|
61
|
48
|
37
|
28
|
21
|
16
|
13
|
12
|
13
|
16
|
21
|
28
|
37
|
48
|
61
|
76
|
-4
|
-5
|
175
|
151
|
129
|
109
|
91
|
75
|
61
|
49
|
39
|
31
|
25
|
21
|
19
|
19
|
21
|
25
|
31
|
39
|
49
|
61
|
75
|
-5
|
-6
|
196
|
171
|
148
|
127
|
108
|
91
|
76
|
63
|
52
|
43
|
36
|
31
|
28
|
27
|
28
|
31
|
36
|
43
|
52
|
63
|
76
|
-6
|
-7
|
219
|
193
|
169
|
147
|
127
|
109
|
93
|
79
|
67
|
57
|
49
|
43
|
39
|
37
|
37
|
39
|
43
|
49
|
57
|
67
|
79
|
-7
|
-8
|
244
|
217
|
192
|
169
|
148
|
129
|
112
|
97
|
84
|
73
|
64
|
57
|
52
|
49
|
48
|
49
|
52
|
57
|
64
|
73
|
84
|
-8
|
-9
|
271
|
243
|
217
|
193
|
171
|
151
|
133
|
117
|
103
|
91
|
81
|
73
|
67
|
63
|
61
|
61
|
63
|
67
|
73
|
81
|
91
|
-9
|
-10
|
300
|
271
|
244
|
219
|
196
|
175
|
156
|
139
|
124
|
111
|
100
|
91
|
84
|
79
|
76
|
75
|
76
|
79
|
84
|
91
|
100
|
-10
|
-10
|
-9
|
-8
|
-7
|
-6
|
-5
|
-4
|
-3
|
-2
|
-1
|
0
|
1
|
2
|
3
|
4
|
5
|
6
|
7
|
8
|
9
|
10
|
Some of the
equalities are due to the fact that x2 + xy + y2 is
commutative, so (x, y) = (y, x) because x2 + xy + y2 = y2
+ yx + x2. Some of the other
equalities are due to the fact that x2 + xy + y2 is
symmetrical, so (x, y) = (-x, -y) because x2 + xy + y2 =
(-x)2 + (-x)(-y) + (-y)2.
The rest of the equalities with -x – y (or x + y) term can also be proved
by substitution. For example, (x, -x –
y) = x2 + x(-x – y) + (-x – y)2 = x2 – x2
– xy + x2 + 2xy + y2 = x2 + xy + y2
= (x, y).
To derive
the equality (x, y) = (x, -x – y), we can let p = x2 + xy + y2
and solve the formula p = x2 + x(y + k) + (y + k)2 for k,
knowing that one solution for k is k = 0, and recognizing that as a quadratic,
k will likely have a second solution. So
solving, x2 + xy + xk + y2 + 2ky + k2 – p = 0,
or k2 + (x + 2y)k + x2 + xy + y2 – p = 0. Since p = x2 + xy + y2,
then k2 + (x + 2y)k = 0, or k(k + (x + 2y)) = 0. So k = 0 (which we already knew) or k = -(x +
2y). If k = -(x + 2y), then the other
coordinate with x would be y + k = y + -(x + 2y) = -x – y.
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