=3/2x( 1/3-1/5+1/5-1/7-1/7+....+ 1/97-1/99)
=3/2x( 1/3-1/99)
=3/2x 32/99
= 16/33
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tính nhanh và ko quy đồng
a] C = \(\frac{5}{2\cdot1}+\frac{4}{1\cdot11}+\frac{3}{11\cdot2}+\frac{1}{2\cdot15}+\frac{13}{15\cdot4}\)
b] B = \(\frac{6}{3\cdot5}+\frac{6}{5\cdot7}+\frac{6}{7\cdot9}+.....+\frac{6}{97\cdot99}\)
A = \(\frac{4}{3\cdot5}+\frac{4}{5\cdot7}+\frac{4}{7\cdot9}+\frac{4}{9\cdot11}\)
Tính nhanh:
\(\frac{33}{2}+\frac{33}{6}+\frac{33}{18}+\frac{33}{54}+\frac{33}{162}+\frac{33}{486}\)
\(\frac{2}{3\cdot5}+\frac{2}{5\cdot7}+\frac{2}{7\cdot9}+\frac{2}{9\cdot11}+\frac{2}{11\cdot13}+\frac{2}{13\cdot15}\)
bài 7:tính bằng cách thuận tiện nhất
a, 1/3+2/3...+3\(\frac{1}{3}\) + 3\(\frac{2}{3}\) =.......
b,9+9/2+9/4+9/8......+9/128+9/256=......
c,\(\frac{5}{3}\) + \(\frac{5}{3\cdot5}\) + \(\frac{5}{5\cdot7}\) + ......... +\(\frac{5}{101\cdot103}\) =.........
\(\frac{2}{1\cdot3}+\frac{2}{3\cdot5}+\frac{2}{5\cdot7}+\frac{2}{7\cdot9}+\frac{2}{9\cdot12}\)
Tìm a biết :
A=\(\frac{3}{4\cdot7}+\frac{3}{7\cdot10}+\frac{3}{10\cdot13}+..........+\frac{3}{94\cdot97}+\frac{3}{97\cdot100}\)=??????????????????
\(\left(\frac{1}{1\cdot3}+\frac{1}{3\cdot5}+\frac{1}{5\cdot7}+\frac{1}{7\cdot9}\right)\cdot\left(x-\frac{1}{2}\right)=\frac{3}{4}\)
Tính nhanh:
A = \(\frac{2}{1\cdot3}+\frac{2}{3\cdot5}+\frac{2}{5\cdot7}+\frac{2}{7\cdot9}+...+\frac{2}{2001\cdot2003}+\frac{2}{2003\cdot2005}\)
Tính nhanh biểu thức sau :
\(\frac{4}{1\cdot3}+\frac{4}{3\cdot5}+\frac{4}{5\cdot7}+\frac{4}{7\cdot9}+....+\frac{4}{15\cdot17}+\frac{4}{17\cdot19}+\frac{4}{19\cdot21}\)