\(\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{98.99}=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{98}-\frac{1}{99}=\frac{1}{2}-\frac{1}{99}=\frac{97}{198}=\frac{a}{198}\)
\(\Rightarrow a=97\)
B = 1 + 2 + 3 + 4 + 5 + ... + 96 + 97 + 98 + 99 + 100
Tính B
A = 2 + 4 + 6 + 8 + 10 + ... + 192 + 194 + 196 + 198 + 200
Tính A
A = 1-2+3-4+5-6+.....+97-98+99-100+101
B = 1+2-3-4+5+6-7-8+......+98-99-100+101
Tính tổng
a, 1 + 2 = 3 + 4 + ....... + 98 + 99
b, 1 + 3 + 5 + 7 + .......... + 97 +99
c, 2 + 4 + 6 + 8 +.........+ 96 + 98
1)Tính:
a)100-99+98-97+.............+4-3+2-1
b)99-97+95-93+...............+7-5+3-1
A= ( 1 + 2 + 3 + 4 + ..........+ 97 + 98 + 99 + 100 ) : 5
Tính nhanh
a,(1+2 +3 +...+99) x (13 x 15 – 12 x 15 –15)
b,2+4+ 6+...+ 98+100–(1+3 +5 +...+97+99)
tính
a, 100 - 99 +98 - 97 + .......................... + 4-3+2-1
b, 99 - 97 + 95 - 93 + ............................ + 7-5+ 3-1
Bài 8:
a)100-99+98-97+..+4-3+2-1=?
b)99-97+95-93+...+7-5+3-1=?
A = (1+2+3+4.........+97+98+99+100) : 5
