do this...

for all integers there are 4 possibilities:

4x, 4x+1, 4x+2, 4x+3.

for 4x, the formula turns out to be 4x**2-4x**2=2, no solution;

for 4x+1, (16x**2+8x+1)/4-4x**2=2x=2, x=1.

for 4x+2, (16x**2+16x+4)/4-4x**2-4X-1=0, no solution;

for 4x+3, (16x**2+24x+9)/4-4x**2-4x-1=2x+1=2, no integer solution.

so the only solution is 5.

所有跟帖： 

• 謝謝您的詳細解答。 -Pilsung- ♂ (0 bytes) () 08/07/2023 postreply 17:58:43

• check 2x+1 就夠了，沒必要看除4的餘數 -STEMkid- ♂ (0 bytes) () 08/07/2023 postreply 18:00:00