\(A< \frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+...+\frac{1}{19\cdot20}\)
\(\Rightarrow A< 1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{99}-\frac{1}{20}\)
\(\Rightarrow A< 1-\frac{1}{20}< 1\)
Bài 1:Tìm x
a, \(2.x-\frac{1}{2}=\frac{5}{4}-\frac{1}{2}.x\)
b, \(\frac{3}{4}-\frac{5}{2}.x=2-3.x\)
c, \(\frac{3}{2}.\left(x-\frac{1}{3}\right)-2\left(x-\frac{1}{2}\right)=3\)
d, \(\frac{4}{3}.\left(x-\frac{3}{2}\right)-3.\left(\frac{1}{3}.x+1\right)=6\)
A=\(\frac{\left(\frac{13}{84}.\frac{1}{4}-\frac{2}{5}.\frac{7}{180}\right):2\frac{7}{18}+4\frac{1}{2}.0.1}{70.5-528:7\frac{1}{2}}\)
1/Tính:
\(\left(2-\frac{1}{5}\right).\left(\frac{-3}{15}+\frac{1}{3}\right)\)
2/Tìm x, biết:
\(\frac{x}{20}-\frac{2}{5}=\frac{4}{15}.\frac{-9}{8}\)
Bài 1:Thực hiện phép tính
a)\(\left(4\frac{4}{9}+3\frac{1}{3}\right).2\frac{1}{4}.2\frac{3}{4}\)
b)( 204,12 : 40,5 - 3,2 . 1.2 ) . \(6\frac{1}{2}\)
c)60% . \(\left(-\frac{5}{22}\right)+0,9:3\frac{2}{3}\)
Tính nhanh tổng\(B=\frac{1}{1+2}+\frac{1}{1+2+3}+\frac{1}{1+2+3+4}+...+\frac{1}{1+2+3+4+...+8}\)
tìm x
a, 2 . x \(\frac{-3}{4}\) = \(\frac{-5}{12}\)
b, \(\frac{2}{3}\) + \(\frac{1}{3}\) . x = 7
c, ( 4 . x + \(\frac{1}{8}\) ) = \(\frac{3}{10}\)
d, \(\frac{1}{3}\) . x - 5 = 1\(\frac{1}{2}\)
e, \(\frac{-2}{3}\) . x + \(\frac{1}{3}\) = \(\frac{-1}{2}\)
tìm x biết:
a.\(\frac{x}{3}\)-\(\frac{1}{2}\)=\(\frac{4}{9}\)
b. \(\frac{1}{5}\)+x:\(\frac{1}{2}\)=\(\frac{3}{4}\)
\(\frac{1}{a}\)-\(\frac{1}{b}\)=\(\frac{2}{143}\);b-a=2 \(\frac{a}{3}\)+\(\frac{1}{6}\)=\(\frac{2}{b}\)
Chứng tỏ rằng:
a) \(S=\dfrac{1}{5}+\dfrac{1}{13}+\dfrac{1}{14}+\dfrac{1}{15}+\dfrac{1}{61}+\dfrac{1}{62}+\dfrac{1}{63}< \dfrac{1}{2}\)
b) \(S=\dfrac{1}{41}+\dfrac{1}{42}+...+\dfrac{1}{80}>\dfrac{7}{12}\)
c) \(S=\dfrac{1}{2}+\dfrac{1}{2^2}+\dfrac{1}{2^3}+...+\dfrac{1}{2^{20}}< 1\)
d) \(\dfrac{49}{100}< S=\dfrac{1}{2^2}+\dfrac{1}{3^2}+\dfrac{1}{4^2}+...+\dfrac{1}{99^2}< 1\)
Các bạn giải ra từng bước dùm mik nha
Thanks m.n
