Question

設(shè)A=37+

C

27

•35+

C

47

•33+

C

67

•3，B=

C

17

•36+

C

37

•34+

C

57

•32+1，則A-B的值為（　�。�

A．128

B．129

C．47

D．0

Answer 1

因?yàn)?span mathtag="math" >(x+1)7=

C

07

x7+

C

17

x6+

C

27

x5+…+

C

67

x+

C

77

，
取x=3，得37+

C

17

36+

C

27

35+…+1=47①
取x=-3，得-37+

C

17

36-

C

27

35+…+1=-2⁷②
①+②除以2得B=

C

17

•36+

C

37

•34+

C

57

•32+1=

47-27

2

，
①-②除以2得A=37+

C

27

•35+

C

47

•33+

C

67

•3=

47+27

2

，
所以A-B=

47+27

2

-

47-27

2

=27=128．
故選A．