Question

[Chibi Yoona]

Bài1:Tính giá trị của biểu thức

a.2/5.1/3-2/15:1/5+3/5.1/3

b.[6+(1/2)³- l-1/2l]:3/12

c.(-1/2)²:1/4-2(-1/2)²

d.F=4/2.4+4/4.6+4/6.8+...+4/2008.2010

e.F=1/18+1/54+1/108+...+1/990

Answer 1

[Nguyễn Lê Phước Thịnh]

a: \(=\dfrac{2}{15}-\dfrac{2}{15}\cdot5+\dfrac{3}{15}=\dfrac{2-10+3}{15}=\dfrac{-5}{15}=\dfrac{-1}{3}\)

b: \(=\left(6+\dfrac{1}{8}-\dfrac{1}{2}\right)\cdot4=\dfrac{48+1-4}{8}\cdot4=\dfrac{45}{2}\)

c: \(=\dfrac{1}{4}\cdot4-2\cdot\dfrac{1}{4}=1-\dfrac{1}{2}=\dfrac{1}{2}\)

d: \(F=2\left(\dfrac{2}{2\cdot4}+\dfrac{2}{4\cdot6}+...+\dfrac{2}{2008\cdot2010}\right)\)

\(=2\left(\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{6}+...+\dfrac{1}{2008}-\dfrac{1}{2010}\right)\)

\(=2\cdot\dfrac{1004}{2010}=\dfrac{1004}{1005}\)