A=(1/2-1/5+1/5-1/8+1/8-....+1/50-1/51)
= 1/2-1/51
= 51/102 - 2/102
= 49/102
B=1.4/1.5.4+1.4/5.9.4+...+1.4/41.45.4
= 1/4(1-1/5+1/5-1/9+1/9-...+1/41-1/45)
= 1/4(1-1/45)
= 1/4.44/45
= 11/45
Nhanh +Đúng = Tick ( gắp )
\(A=\frac{1}{2.5}\frac{1}{5.8}\frac{1}{8.11}\frac{1}{11.14}\frac{1}{14.17}\frac{1}{17.20}\)
\(B=8400.\left(\frac{1}{1.5}+\frac{1}{5.9}+\frac{1}{9.13}+\frac{1}{13.17}+\frac{1}{17.21}+\frac{1}{21.25}\right)\)
b) \(x+\frac{4}{5.9}+\frac{4}{9.13}+...+\frac{4}{41.45}=1\)
Bài 1Tìm x biết
\(x-\frac{37}{45}=\frac{4}{5.9}+\frac{4}{9.13}+...+\frac{4}{41.45}\)
Bài 2 Tính giá trị các biểu thức sau
a) A = \(\frac{1+\frac{1}{3}+\frac{1}{5}+...+\frac{1}{97}+\frac{1}{99}}{\frac{1}{1.99}+\frac{1}{3.97}+\frac{1}{5.95}+...+\frac{1}{97.3}+\frac{1}{99.1}}\)
b) B = \(\frac{\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+...+\frac{1}{100}}{\frac{99}{1}+\frac{98}{2}+\frac{97}{3}+...+\frac{1}{99}}\)
Tìm các số nguyên x biết a.\(\frac{7}{x}+\frac{4}{5.9}+\frac{4}{9.13}+...+\frac{4}{41.45}=\frac{29}{45}\)
b.\(1+\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+...+\frac{1}{x\left(x+2\right):2}=\frac{4120}{2011}\)
Tìm số tự nhiên x, biết:
a, \(x-\frac{20}{11.13}-\frac{20}{13.15}-\frac{20}{15.17}-....-\frac{20}{53-55}=\frac{3}{11}\)
b, \(x+\frac{4}{5.9}+\frac{4}{9.13}+\frac{4}{13.17}+...+\frac{4}{41.45}=\frac{-37}{45}\)
c,\(\frac{1}{21}+\frac{1}{28}+\frac{1}{36}+\frac{2}{x\left(x+1\right)}=\frac{2}{9}\)
\(B=\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{197.200}\)
\(C=\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{97.99}\)
\(D=\frac{1}{1.5}+\frac{1}{5.9}+\frac{1}{9.13}+...+\frac{1}{101.105}\)
\(E=\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}+...+\frac{1}{99.101}\)
Tính :
\(A=8400.\left(\frac{1}{1.5}+\frac{1}{5.9\cdot}+\frac{1}{9.13}+\frac{1}{13.17}+\frac{1}{17.21}+\frac{1}{21.25}\right)\)
II) Tính nhanh:
a)\(\frac{3^2}{1.4}+\frac{3^2}{4.7}+\frac{3^2}{7.10}+...+\frac{3^2}{61.64}\)
b)\(\frac{1}{1.5}+\frac{1}{5.9}+\frac{1}{9.13}+...+\frac{1}{21.25}\)
c)\(\frac{2^2}{1.3}+\frac{3^2}{2.4}+\frac{4^2}{3.5}+...+\frac{20^2}{19.21}\)
nhanh choa tick * đg rất tức giận*
\(\frac{3}{1.5}+\frac{3}{5.9}+\frac{3}{9.13}+...+\frac{3}{21.25}\)
