\(x+\dfrac{4}{5.9}+\dfrac{4}{9.13}+...+\dfrac{4}{41.45}=-\dfrac{37}{45}\\ x+\left(\dfrac{1}{5}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{13}+...+\dfrac{1}{44}-\dfrac{1}{45}\right)=-\dfrac{37}{45}\\ x+\left(\dfrac{1}{5}-\dfrac{1}{45}\right)=-\dfrac{37}{45}\\ x+\dfrac{8}{45}=-\dfrac{37}{45}\\ x=-\dfrac{37}{45}-\dfrac{8}{45}\\ x=-1\)
BT3: Tìm x, biết
3) \(\dfrac{3}{4}.x-\dfrac{5}{3}.x=\dfrac{7}{12}\)
4) \(x-\dfrac{1}{7}=\) \(\dfrac{\dfrac{4}{2011}-\dfrac{4}{2013}+\dfrac{4}{99}}{\dfrac{5}{2011}-\dfrac{5}{2013}+\dfrac{5}{99}}+\dfrac{1}{2}\)
Các bạn giúp mk nhé
BT3: Tìm x, biết:
7) \(\dfrac{-5}{17}+\dfrac{3}{17}\le\dfrac{x}{17}\le\dfrac{13}{17}+\dfrac{-11}{17}\)
8) \(\dfrac{2}{3}\left(\dfrac{1}{2}+\dfrac{3}{4}-\dfrac{1}{3}\right)\le\dfrac{x}{18}\le\dfrac{7}{3}\left(\dfrac{1}{2}-\dfrac{1}{6}\right)\)
BT3: Tìm x, biết
9) \(\dfrac{x}{9}< \dfrac{7}{x}< \dfrac{x}{6}\) ( với x \(\in\) N*
10) \(\dfrac{7}{x}< \dfrac{x}{4}< \dfrac{10}{x}\) ( với x \(\in\) N*)
tính:
\(\dfrac{2}{5}x\dfrac{1}{3}-\dfrac{2}{15}:\dfrac{1}{5}+\dfrac{3}{5}x\dfrac{1}{3}\)
2)\(\left(3\dfrac{1}{3}+2,5\right):\left(3\dfrac{1}{6}-4\dfrac{1}{5}\right)-\dfrac{11}{31}\)
3)\(\left[6+\left(\dfrac{1}{2^{ }}\right)^3-\left|-\dfrac{1}{2}\right|\right]:\dfrac{3}{12}\)
4)\(\dfrac{18}{37}+\dfrac{8}{24}+\dfrac{19}{37}-1\dfrac{23}{24}+\dfrac{2}{3}\)
5) \(\left(-2\right)^3x\left(\dfrac{3}{4}-0,25\right):\left(2\dfrac{1}{4}-1\dfrac{1}{6}\right)\)
6)\(\left(\dfrac{2}{5}\right)^2+5\dfrac{1}{2}x\left(45-2\right)+\dfrac{23}{-4}\)
7)\(\dfrac{4}{9}-19\dfrac{1}{3}-\dfrac{4}{9}x39\dfrac{1}{3}\)
8)\(\left(-\dfrac{1}{2}\right)^2:\dfrac{1}{4}-2x\left(-\dfrac{1}{2}\right)^2\)
9)\(125\%x\left(-\dfrac{1}{2}\right)^3:\left(1\dfrac{5}{16}-1,5\right)+2008^0\)
giúp mình nha mai mình học rùi 
Tính :
A = 1 - \(\dfrac{4}{5.7}-\dfrac{4}{5.9}-\dfrac{4}{9.11}-......-\dfrac{4}{59.61}\)
Bài 1 : Tìm x
a) 4\(\dfrac{1}{2}\)x : \(\dfrac{5}{12}\)=0,5 b)1,5+1\(\dfrac{1}{4}\).x= \(\dfrac{2}{3}\) c) 7,5.1\(\dfrac{3}{4}\)=\(6\dfrac{2}{5}\) d)(x - 5):\(\dfrac{1}{3}\)=\(\dfrac{2}{5}\) e) (4,5-2x):\(\dfrac{3}{4}\)=1\(\dfrac{1}{3}\) f) (2,7x - 1\(\dfrac{1}{2}\)x) : \(\dfrac{2}{7}=\dfrac{-21}{7}\)
Bài 2 : tìm a,b biết
\(\dfrac{a}{27}=\dfrac{-5}{9}=\dfrac{-45}{b}\)
Sử dụng điều kiện \(\dfrac{n}{a\left(a+n\right)}=\dfrac{1}{a}-\dfrac{1}{a+n}\) để tính:
a. \(A=\dfrac{1}{2.9}+\dfrac{1}{9.7}+\dfrac{1}{7.19}+...+\dfrac{1}{252.509}\)
b.\(B=\dfrac{2}{4.7}-\dfrac{3}{5.9}+\dfrac{2}{7.10}-\dfrac{3}{9.13}+...+\dfrac{2}{301.304}-\dfrac{3}{401.405}\)
BT3: Tìm x, biết
1) \(\dfrac{5}{3}-x+\dfrac{1}{5}=\dfrac{-3}{10}\)
2) \(\dfrac{11}{12}-\left(\dfrac{2}{5}+x\right)=\dfrac{2}{3}\)
BT2: Tính nhanh:
5) \(\dfrac{15}{7}\left(\dfrac{1}{5}-\dfrac{46}{45}\right)+\dfrac{46}{45}\left(\dfrac{15}{7}-\dfrac{45}{46}\right)\)
6) \(\dfrac{43}{47}\left(\dfrac{18}{37}+\dfrac{47}{43}\right)-\dfrac{18}{37}\left(\dfrac{43}{47}+\dfrac{37}{36}\right)\)