A.7                 B.8                 C.9                  D.10

A.1                 B.2                  C.3                     D.4

A.                               B.

C.+                 D.-

A.6+6·7^k               B.2+7^k-1              C.2(2+7^k+1)             D.3(2+7^k)

(1)当n=1时, ＜1+1,不等式成立.

(2)假设当n=k(k∈N*)时,不等式成立,即＜k+1,则当n=k+1时, ＜,

∴当n=k+1时,不等式成立.

上述证法(    )

A.过程全部正确

B.n=1验得不正确

C.归纳假设不正确

D.从n=k到n=k+1的推理不正确

A.2π               B.π                  C.                    D.

A.1+2+2²+…+2^k-1=2^k+1-1

B.1+2+2²+…+2^k+2^k+1=2^k-1+2^k+1

C.1+2+2²+…+2^k-1+2^k+1=2^k+1-1

D.1+2+2²+…+2^k-1+2^k=2^k-1+2^k