In: Math
A parallelogram has consecutive sides with lengths 9 and 7 and diagonals of integral length How long are these diagonals?
By the properties of the parallelogram, d12 + d22 = 2a2 + 2b2, where d1 and d2 are the diagnols of the parallelogram and a and b are the lengths of the sides of the parallelogram.
Here a = 9 and b = 7
Therefore d12 + d22 = 2*92 + 2*72 = (2 * 81) + (2 * 49) = 162 + 98 = 260
Since the diagnols are integers therefore they have to be perfect squares whose sum is = 260
d12 | d22 | d12+d22 | d1 | d2 |
1 | 259 | 260 | 1 | 16.093477 |
4 | 256 | 260 | 2 | 16 |
9 | 251 | 260 | 3 | 15.84298 |
16 | 244 | 260 | 4 | 15.620499 |
36 | 224 | 260 | 6 | 14.96663 |
49 | 211 | 260 | 7 | 14.525839 |
64 | 196 | 260 | 8 | 14 |
81 | 179 | 260 | 9 | 13.379088 |
100 | 160 | 260 | 10 | 12.649111 |
121 | 139 | 260 | 11 | 11.789826 |
144 | 116 | 260 | 12 | 10.77033 |
169 | 91 | 260 | 13 | 9.539392 |
196 | 64 | 260 | 14 | 8 |
225 | 35 | 260 | 15 | 5.9160798 |
296 | -36 | 260 | 17.204651 | #NUM! |
We see only two cases cropping up, where both diagnols are integers.
Case 1: d1 = 2 and d2 = 16. This can be discarded as the lengths of the diagnol 1 is too small to form a parallelogram.
Case 2: d1 = 8 and d2 = 14. This is the correct and only possible option.