a*6=b*5
a*7-b*4=2200
a=?;b=?
Tính : 1/26+1/27+1/28+.......+1/50=1-1/2+1/3-1/4+.....+1/491/26+1/27+1/28+.......+1/50=1-1/2+1/3-1/4+.....+1/49
không dùng máy tính, hãy tính : 1+1+1++1+1+1+1+1+1+1+1+1+111+1+1+1+1+1+1+1+1+1+1+323+121-1+5+66564+35+5565+2+2 = ?????
1) CMR : 1-1/2+1/3-1/4+.....+1/1317-1/1318+1/1319=1/660+1/661+...+1/1319
2)Cho a/b= 1+1/2+1/3+1/4+....+1/11+1/12
CMR : a chia hết cho 13
{1-1/2}x{1-1/3}x{1-1/4}x{1-1/5}x......x{1-1/2017}x{1-1/2018}
b,(1-1/49)x(1-1/64)x(1-1/81)x(1-1/100)x(1-1/121)x(1-1/144)
1/2*1/3+1/3*1/4+1/4*1/5+1/5*1/6+1/6*1/7+1/7*1/8
Tìm x biết:
1. 9/4:(1/3x-1/2)=4 và 1/2
2. 1/2015.x=(1-1/2) (1-1/3) (1-1/4)...(1-1/2014) (1-1/2015)
bai 1: Tinh nhanh
a) 1/2 + 1/4 + 1/8 + 1/16 + 1/32
b) 1/2 x 1/2 + 1/2 x 1/3 + 1/3 + 1/3 + 1/4 + 1/4 x 1/5 + 1/5 x 1/6
Chứng tỏ: 1- 1/2 + 1/3 - 1/4 + 1/5 - 1/6 +.........+ 1/99 - 1/100 = 1/51 + 1/52 + 1/53 + .....+ 1/100