Sunday, November 2, 2014

The Function x^2 + xy + y^2 – Part 7

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.  

No comments:

Post a Comment