Question

式子

C

15

+2

C

25

+2

C

35

+2

C

45

+

C

55

的值是______．

Answer 1

C

15

+2

C

25

+2

C

35

+2

C

45

+

C

55

=5+2×

5×4

2

+2×

5×4×3

3×2×1

+10+1=5+20+20+10+1=56
故答案为：56