\(B=\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+..+\frac{3}{97.100}\)
\(=\frac{1}{1}-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-....+\frac{1}{94}-\frac{1}{97}+\frac{1}{97}-\frac{1}{100}\)
\(=\frac{1}{1}-\frac{1}{100}\)
\(=\frac{100}{100}-\frac{1}{100}\)
\(=\frac{99}{100}\)
Tính nhanh
A=\(\frac{3^2}{1.4}+\frac{3^2}{4.7}+\frac{3^2}{7.10}+.....+\frac{3^2}{97.100}\)
Giúp tớ quới làm rùi mà cứ thấy sai sai
Tính A=3^2/1.4+3^2+4.7+3^2+7.10+...+3^2/97.100
Tính nhanh
A=3^2/1.4+3^2/4.7+3^2/7.10+....+3^2/97.100
A=\(\dfrac{3^2}{1.4}+\dfrac{3^2}{4.7}+\dfrac{3^2}{7.10}+\dfrac{3^2}{10.13}+\dfrac{3^2}{13.16}+...+\dfrac{3^2}{97.100}\)
Cho A=\(\frac{4}{1.4}+\frac{4}{4.7}+\frac{4}{7.10}+..............+\frac{4}{67.70}\)
Chứng minh A>\(\frac{9}{7}\)
Tìm x
a / (6 \(\frac{2}{7}\) .x + \(\frac{3}{7}\) ): 2\(\frac{1}{5}\) - \(\frac{3}{7}\) = -1
b/ 5 \(\frac{8}{17}\) : x + (- \(\frac{1}{17}\)): x + 3 \(\frac{1}{17}\): 17\(\frac{1}{3}\)= \(\frac{4}{17}\)
c/ \(\frac{1}{1.4}\)+\(\frac{1}{4.7}\)+\(\frac{7}{7.10}\)+ ...+ \(\frac{1}{x\left(x+3\right)}\)= \(\frac{6}{19}\)
5 Tinh tong
S=\(\dfrac{3}{1.4}\)+\(\dfrac{3}{4.7}\)+\(\dfrac{3}{7.10}\)+...+\(\dfrac{3}{97.100}\)
Tìm x
a/ \(\frac{-9}{46}\)- 4\(\frac{1}{23}\): (3\(\frac{1}{4}\)-x: \(\frac{3}{5}\))+2\(\frac{8}{23}\)= 1
b/ 5\(\frac{8}{17}\): (\(\frac{-1}{17}\)): + 3\(\frac{1}{17}\):17\(\frac{1}{3}\)= \(\frac{4}{17}\)
c/ \(\frac{1}{1.4}\)+ \(\frac{1}{4.7}\)+ \(\frac{1}{7.10}\)+ ....+ \(\frac{1}{x\left(x+3\right)}\)= \(\frac{6}{19}\)
Tính
S=2/1.4+2/4.7+2/7.10+....+2/97.100