Sửa đề: \(\left(\dfrac{1}{3}+\dfrac{3}{4}-\dfrac{13}{12}\right):\left(\dfrac{12}{23}+\dfrac{123}{234}+\dfrac{1234}{2345}\right)\)
\(=\left(\dfrac{4+9-13}{12}\right):\left(\dfrac{12}{23}+\dfrac{123}{234}+\dfrac{1234}{2345}\right)\)
=0
Rút gọn: B = \(\left(1-\dfrac{1}{2}\right).\left(1-\dfrac{1}{3}\right).\left(1-\dfrac{1}{4}\right)....\left(1-\dfrac{1}{20}\right)\)
Tính:
a) \(\dfrac{-5}{6}+\dfrac{1}{6}\)
b) \(\dfrac{1}{3}-\dfrac{5}{4}.\dfrac{4}{15}\)
c) \(4.\left(-5\right)^2+\left(-2\right)^3.25\)
d) \(\dfrac{-2}{7}+\dfrac{1}{5}:\dfrac{7}{15}\)
Tìm x:
a) \(x\) + \(\dfrac{-3}{7}=\dfrac{4}{7}\).
b) \(\dfrac{1}{2}x-75\%=\dfrac{1}{4}.\)
c) \(\left|x-\dfrac{2}{3}\right|+2,25=\dfrac{3}{4}\).
Tính
a, \(1\dfrac{7}{20}\) : 2,7+2,7:1,35+(0,4:\(2\dfrac{1}{2}\) ) . (4,2-\(1\dfrac{3}{40}\) )
b, \(\left(6\dfrac{3}{5}-3\dfrac{3}{14}\right).5\dfrac{5}{6}:\left(21-1.25\right):2,5\)
c,\(\dfrac{0,125-\dfrac{1}{5}+\dfrac{1}{7}}{0,375-\dfrac{3}{5}+\dfrac{3}{7}}+\dfrac{\dfrac{1}{2}+\dfrac{1}{3}-0,2}{\dfrac{3}{4}+0,5-\dfrac{3}{10}}\)
tính bằng cách hợp lý
A=\(\dfrac{-2}{3}+\dfrac{5}{3}:10-\dfrac{1}{27}\times\left(-3\right)^2\)
1) Chứng minh rằng : \(\dfrac{1}{2^2}+\dfrac{1}{2^3}+\dfrac{1}{2^4}+...+\dfrac{1}{2^n}< 1\)
2) Cho : \(A=\dfrac{8n+193}{4n+3}\)
Tìm n ϵ N để : a) A là số tự nhiên.
b) A là phân số tối giản.
3) Tìm các số nguyên tố x, y biết : \(\left(x-2\right)^2.\left(y-3\right)^2=-4\)
4) Tìm x ∈ N biết : \(\left(x-5\right).\dfrac{30}{100}=\dfrac{20.x}{100}+5\)
1, \(\dfrac{1}{2.\left(x+1\right)}\) = \(\dfrac{1}{6}\) ;
2, 1 < \(\dfrac{x}{5}\) \(\le2\) ;
3, \(\dfrac{5}{5}< \dfrac{x}{5}< \dfrac{ }{5}\)
a,1+5+9+13+16+....+x=501501
b,\(\left(x-\dfrac{1}{3}\right)^2-\dfrac{1}{4}=0\)
c,\(2^x+642=5^y\)
d,x+(x+1)+(x+2)+....+(x+30)=1240
1)Cho B=\(\dfrac{1}{4}+\dfrac{1}{5}+\dfrac{1}{6}+...+\dfrac{1}{19}\).Chứng minh B>1
2)Tính nhanh:M=\(\dfrac{\dfrac{3}{5}+\dfrac{3}{7}-\dfrac{3}{11}}{\dfrac{4}{5}+\dfrac{4}{7}-\dfrac{4}{11}}\)
