a) (100 - 99) + (98 - 97) + ... + (2 - 1) = 1 + 1 + ... + 1 = 50
b) (200 - 199) + (198 - 197) + ... + (2 - 1) = 1 + 1 + ... + 1 = 100
Tính giá trị biểu thức A , biết rằng A = M : N
Mà M = \(\dfrac{\dfrac{1}{99}+\dfrac{2}{98}+\dfrac{3}{97}+\dfrac{4}{96}+...+\dfrac{97}{3}+\dfrac{98}{2}+\dfrac{99}{1}}{\dfrac{1}{2}+\dfrac{1}{3}+\dfrac{1}{4}+\dfrac{1}{5}+\dfrac{1}{6}+...+\dfrac{1}{100}}\)
N = \(\dfrac{92-\dfrac{1}{9}-\dfrac{2}{10}-\dfrac{3}{11}-...-\dfrac{90}{98}-\dfrac{91}{99}-\dfrac{92}{100}}{\dfrac{1}{45}+\dfrac{1}{50}+\dfrac{1}{55}+...+\dfrac{1}{495}+\dfrac{1}{500}}\)
tính tỉ số \(\frac{A}{B}\)biết:
A=\(\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+...+\frac{1}{200}\)
B=\(\frac{1}{199}+\frac{2}{198}+\frac{3}{197}+...+\frac{198}{2}+\frac{199}{1}\)
1002-992+982-972+962-952+..........+22-12
Nguyễn Thành Trương Lê Thanh Nhàn
Tính tổng
1,A=a1+a2+...+an với ai-ai-1=k
2,B=1/1*2*3+1/2*3*4+...+1/48*49*50
3,C=1+1/3+1/5+...+1/97+1/99
/
1/1*99+1/3*97+...+1/97*3+1/99*1
Rút gọn
A= 5 + 5^2 + .....+ 5^200
B= 2^100 - 2^99 + 2^98 - 2^97 +.....+ 2^2 - 2
Chứng tỏ rằng :1-1/2+1/3+1/4+...+1/99-1/200=1/101+1/102+...+1/199+1/200 .
B=3100-399+398-397+....+32-3+1
Rút gọn :
A = \(3^{100}-3^{99}+3^{98}-3^{97}+......+3^2-3+1\)
Tính tổng :
a) 12+22+32+42+...992+1002
b) 12+32+52+72+...972+992
