D = 31 - 32 + 33 - 34 + .... + 32001 - 32002 + 32003
3D = 32 - 33 + 34 - 35 + .... + 32002 - 32003 + 32004
3D + D = (32 - 33 + 34 - 35 + ... + 32002 - 32003 + 32004) + (31 - 32 + 33 - 34 + ... + 32001 - 32002 + 32003)
4D = 32004 + 31
D = \(\frac{3^{2004}+3^1}{4}\)
Ủng hộ mk nha !!! ^_^