\(=\dfrac{2}{3}\left(\dfrac{3}{1\cdot4}+\dfrac{3}{4\cdot7}+...+\dfrac{3}{31\cdot34}\right)\)
\(=\dfrac{2}{3}\left(1-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+...+\dfrac{1}{31}-\dfrac{1}{34}\right)\)
\(=\dfrac{2}{3}\cdot\dfrac{33}{34}=\dfrac{11}{17}\)
\(=\dfrac{2}{3}\left(\dfrac{3}{1\cdot4}+\dfrac{3}{4\cdot7}+...+\dfrac{3}{31\cdot34}\right)\)
\(=\dfrac{2}{3}\left(1-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+...+\dfrac{1}{31}-\dfrac{1}{34}\right)\)
\(=\dfrac{2}{3}\cdot\dfrac{33}{34}=\dfrac{11}{17}\)
Tính : 2/1x4+2/4x7+2/7x10+......+2/100x103
thưc hiện phép tính 2/1x4+ 2/ 4x7+2/7x10+...2/37x40
Bài 3 :
D = \(\frac{2}{1x4}+\frac{2}{4x7}+\frac{2}{7x10}+...+\frac{2}{97x100}\)
E=2/1x4 + 2/4x7 + 2/7x10 +......+2/100x103
Giải đầy đủ
a)2/1x4+2/4x7+2/7x10+...+2/97x100
b)3/1x5+3/5x9+3/9x13+...+3/97x101
giúp mk nốt câu này luôn nha các bạn vì mk đang cần rất rất chi là gấp luôn í!
m=3/(1x4) + 3/(4x7) + 3/(7x10) + ... + 3/(19x22)
3/1x4+3/4x7+3/7x10+...+3/nx(n+3)
tinh nhanh 1/1x4 + 1/4x7 +1/7x10 +...+ 1/91x94
tinh nhanh 1/1x4 + 1/4x7 +1/7x10 +...+ 1/91x94