B=1/1x4+1/4x3+1/3x8+...+1/7x16+1/16x9+1/9x20
2B=2x(1/4+1/12+1/24+...+1/112+1/144+1/180
2B=2/8+2/24+2/48+...+2/224+2/288+2/360
2B=2/2x4+2/4x6+2/6x8+...+2/14x16+2/16x18+2/18x20
2B=1/2-1/4+1/4-1/6+1/6-1/8+...+1/14-1/16+1/16-1/18+1/18-1/20
2B=1/2-1/20
2B=9/20
B=9/20:2
B=9/40
Bài 1 : tính hợp lý :
a) A = \(\frac{1}{1.4}+\frac{1}{4.7}+\frac{1}{7.10}+\frac{1}{10.13}+\frac{1}{13.16}+\frac{1}{16.19}\)
b) B = \(\frac{1}{32}+\frac{1}{96}+\frac{1}{192}+\frac{1}{320}+\frac{1}{480}\)
Bài 1 : tính hợp lý :
a) A = \(\frac{1}{1.4}+\frac{1}{4.7}+\frac{1}{7.10}+\frac{1}{10.13}+\frac{1}{13.16}+\frac{1}{16.19}\)
b) B = \(\frac{1}{32}+\frac{1}{96}+\frac{1}{192}+\frac{1}{320}+\frac{1}{480}\)
\(B=2016:\left(\frac{0.4-\frac{2}{9}+\frac{2}{11}}{1.4-\frac{7}{9}+\frac{7}{11}}.\frac{-1\frac{1}{6}+0.875-0.7}{\frac{1}{3}-0.25+\frac{1}{5}}\right)\)
Tìm x thỏa mãn
a, \(\frac{1}{1.4}+\frac{1}{4.7}+...+\frac{1}{97.100}=|\frac{x}{3}|\)
b, \(\frac{4}{1.5}+\frac{4}{5.9}+...+\frac{4}{97.101}=|\frac{5x-4}{101}|\)
c,\(\left(1-\frac{1}{2}\right)\left(1-\frac{1}{3}\right)\left(1-\frac{1}{4}\right)...\left(1-\frac{1}{100}\right)=|x-1\frac{99}{100}|\)
Tính nhanh: \(B=\left(\frac{0.4-\frac{2}{9}+\frac{2}{11}}{1.4-\frac{7}{9}+\frac{7}{11}}-\frac{\frac{1}{3}-0.25+\frac{1}{5}}{1\frac{1}{6}-0.875+0.7}\right):\frac{2014}{2015}\)
Tìm x, biết:
\(\frac{1}{1.4}+\frac{1}{4.7}+\frac{1}{7.10}+...+\frac{1}{x\left(x+3\right)}=\frac{125}{376}\)
Tìm |x| biết :
a)x=\(-1\frac{1}{5}\)
b)\(x+25\frac{1}{2}=0\)
c)\(\frac{1}{1.3}+\frac{1}{3.5}+...+\frac{1}{47.49}=\frac{1}{x}\)
d)\(\frac{1}{1.4}+\frac{1}{4.7}+...+\frac{1}{97.100}=\frac{x}{2}\)
1) Tinh gia tri cua bieu thuc:
A=\(\frac{\left(1+2+...+100\right)\left(\frac{1}{2}-\frac{1}{3}-\frac{1}{4}-\frac{1}{5}\right)\left(2,4.42-21.4,8\right)}{1+\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+...+\frac{1}{100}}\)
B=\(\frac{4^6.9^5+6^9.120}{-8^4.3^{12}+6^{11}}\)
Thực hiện phép tính hợp lí nếu có thể:
\(\frac{221}{240}+\frac{1}{3.8}+\frac{1}{6.12}+\frac{1}{9.16}+.....+\frac{1}{54.76}+\frac{1}{57.80}\)
