a: \(A=\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{1}{8}+\dfrac{1}{16}+\dfrac{1}{32}\)
\(2A=1+\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{1}{8}+\dfrac{1}{16}\)
=>A=1-1/32=31/32
b: \(=2\left(\dfrac{1}{1\cdot2}+\dfrac{1}{2\cdot3}+...+\dfrac{1}{19\cdot20}\right)\)
\(=2\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{19}-\dfrac{1}{20}\right)=2\cdot\dfrac{19}{20}=\dfrac{19}{10}\)
tính nhanh biểu thức sau
A.1/2+1/4+1/8+1/16+1/32
B.2/1.2+2/2.3+2/3.4+......+2/18.19+2/19.20
2/1.2 + 2/2.3 + 2/3.4 + .....+2/18.19 + 2/19.20
Tính\(A=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{18.19}+\frac{1}{19.20}\)
tính tổng :
1/2.1 + 1/2.3 + 1/3.4 + ... + 1/18.19 + 1/19.20
Tính \(A=\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{18.19}+\frac{1}{19.20}\)
tìm x trong biểu thức sau
(1/1.2=1/2.3+1/3.4+.....+1/8.9=1/9.10).100-[5/2:(x+206/100)]:1/2=89
Tinh nhanh
B = 4,5 . 19,375 . 0,4 / 3,125 . 1,2 . 1,5 . 6,2
C =1/ 1.2 + 1/ 2.3 + 1/ 3.4 +......+ 1/ 110.11
D = 1/2 + 1/4 + 1/8 + 1/16 +....+ 1/256
Tính nhanh:\(\frac{2}{1.2}+\frac{2}{2.3}+\frac{2}{3.4}+\frac{2}{4.5}+...+\frac{2}{19.20}\)
1.Tính nhanh
A=1+2+3+...+2018;B=1+3+5+...+2017;C=2+4+6+...+2018
D=72.153+27.153+153;E=1.2+2.3+3.4+...+49.50
tính nhanh:
B=1+2+4+5+7+8+10+...+119+121+122
C=1.2+2.3+3.4+...+58.59+59.60
