Câu 5. Tính
1
1
1
a) A=
1 1-3-5-7-...-49
+
+
+...+
4.9 9.14 14.19
44.49
89
b) B=1+ (1+2)+(1+2+3)+.
1
+ (1+2+ .+20)
20
3 3
c) C=
1,5+1-0,75
5
0,375-0,3++
11 12
1890
+
+115
2,5+ -1,25 -0,625+0,5-
5 5
2005
3
11 12
d) D=50+ +
+
50 25 20 10 100
++
3 3 4 3 6.7
100
1
+ +
+
98.99 99