1,A(n)+A(n+1)=4/(3^n) ,同时乘以 (-1)^(n+1) ,
得到 An+1·(-1)^(n+1) -An·(-1)^n = (-4)·(-1/3)^n
设Bn=An·(-1)^n,则有Bn+1 - Bn = (-4)·(-1/3)^n ,且B1 = -1
B2 -B1 = (-4)·(-1/3)^1
B3 - B2 =(-4)·(-1/3)^2
...Bn - Bn-1 =(-4)·(-1/3)^(n-1)
累加 :Bn - B1 = (-4)·(-1/3)^1 + (-4)·(-1/3)^2 + ...+(-4)·(-1/3)^(n-1)
得出Bn = 2 - (-1/3)^(n-1)
然后乘以(-1)^n 得到 An = 2·(-1)^n + (1/3)^n
所以LZ 你的通项算错了...