问题
选择题
|
答案
+1 22-1
+1 32-1
+…+1 42-1 1 (n+1)2-1
=
+1 (2+1)(2-1)
+1 (3+1)(3-1)
+…+1 (4+1)(4-1) 1 (n+1+1)(n+1-1)
=
+1 3×1
+1 4×2
+…+1 5×3 1 (n+2)n
=
[(1-1 2
)+(1 3
-1 2
) +(1 4
-1 3
)+…+ (1 5
-1 n
)+(1 n+2
-1 2
)+(1 4
-1 3
)+…+(1 5
-1 n
)]1 n+2
=
(1+1 2
-1 2
-1 n+1
)1 n+2
=
-3 4
(1 2
+1 n+1
).1 n+2
故选C.