Tính nhanh 2/3x5+2/5x7+2/7x9+2/9x11+2/11x13+2/13x15 +2/1x2+2/2x3+2/3x4+.........+2/8x9+2/9x10
1/1x2+1/2x3+1/3x4+............+1/8x9
1/1x2+1/2x3+1/3x4+...+1/8x9+1/9x10
tinh thuan tien
1/1x2+1/2x3+1/3x4+............+1/7x8+1/8x9+1/9x10
Bài 1. Tính nhanh :
2/1x2 + 2/2x3 + 2/3x4 + ... + 2/18x19 +2/19x20 .
Bài 2. Tìm x trong biểu thức sau :
( 1/1x2 + 1/2x3 + 1/3x4 + ... + 1/8x9 + 1/9x10 ) x 100 - [5/2 : ( x + 206/100 )] :1/2 = 89
CÁC BẠN GIÚP MÌNH NHA !
(1/1x2+1/2x3+1/3x4+........+1/8x9+1/9x10)x100-(5/2:x+(206/100:1/2)
\(\frac{1}{1x2}+\frac{1}{2x3}+\frac{1}{3x4}+\frac{1}{4x5}+..............+\frac{1}{8x9}=?\)
A=\(\frac{1}{1x2}+\frac{1}{2x3}+\frac{1}{3x4}+...+\frac{1}{8x9}\)
a=1/1x2 + 1/2x3+ 1/3x4 +...1/99x100
b=4/1x3+4/3x5+4/5x7 +...+4/51x53
