(1−1/2+1/4−1/6+1/8−1/10+…+1/96−1/98+1/100)×10的整数部分是_.
问题描述:
(1−
+1 2
−1 4
+1 6
−1 8
+…+1 10
−1 96
+1 98
)×10的整数部分是______. 1 100
答
设原式=N,则N=5(2-1+
-1 2
+1 3
-…-1 4
+1 49
),1 50
N<5(2-1+
-1 2
+1 3
-1 4
+1 5
−1 6
)=1 7
<7,83 12
(
-1 7
)+(1 8
-1 9
)+…+(1 10
−1 49
)>0,1 50
所以N>5(2-1+
-1 2
+1 3
-1 4
)=1 5
>6,73 12
即7>N>6,
也就是N=6.…,整数部分是6,
答:整数部分为6.