2,
\(M=\dfrac{\dfrac{3}{5}+\dfrac{3}{7}-\dfrac{3}{11}}{\dfrac{4}{5}+\dfrac{4}{7}-\dfrac{4}{11}}\) =\(\dfrac{3\left(\dfrac{1}{5}+\dfrac{1}{7}-\dfrac{1}{11}\right)}{4\left(\dfrac{1}{5}+\dfrac{1}{7}-\dfrac{1}{11}\right)}\)
\(=\dfrac{3}{4}\)
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) \(\dfrac{-2}{7}+\dfrac{1}{5}:\dfrac{7}{15}\)
Chứng tỏ rằng B = \(\dfrac{1}{2^2}+\dfrac{1}{3^2}+\dfrac{1}{4^2}+\dfrac{1}{5^2}+\dfrac{1}{6^2}+\dfrac{1}{7^2}+\dfrac{1}{8^2}< 1\)
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,\(\dfrac{0,125-\dfrac{1}{5}+\dfrac{1}{7}}{0,375-\dfrac{3}{5}+\dfrac{3}{7}}+\dfrac{\dfrac{1}{2}+\dfrac{1}{3}-0,2}{\dfrac{3}{4}+0,5-\dfrac{3}{10}}\)
Tìm x:
a) \(x\) + \(\dfrac{-3}{7}=\dfrac{4}{7}\).
b) \(\dfrac{1}{2}x-75\%=\dfrac{1}{4}.\)
c) \(\left|x-\dfrac{2}{3}\right|+2,25=\dfrac{3}{4}\).
a,CMR
M=(\(2012+2012^2+2012^3+...+2012^{2010}\))chia hết cho 20
b,Cho
A=\(\dfrac{4}{7.31}+\dfrac{6}{7.41}+\dfrac{9}{10.41}+\dfrac{7}{10.57}\)
B=\(\dfrac{7}{19.31}+\dfrac{5}{19.43}+\dfrac{3}{23.43}\dfrac{11}{23.57}\)
Tính tỉ số \(\dfrac{A}{B}\)
Tìm số nguyên x,y biết
a \(\dfrac{1}{x}=\dfrac{1}{6}+\dfrac{y}{3}\)
b\(\dfrac{x}{8}-\dfrac{2}{y}=\dfrac{3}{4}\)
c\(\dfrac{2x+5}{5}=\dfrac{x}{5}\)
(\(\dfrac{9}{2}\) -2x).1\(\dfrac{4}{7}\) =\(\dfrac{11}{4}\)
Các bn giúp mik với !
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 : \(\left(x-5\right).\dfrac{30}{100}=\dfrac{20.x}{100}+5\)
Rút gọn: B = \(\left(1-\dfrac{1}{2}\right).\left(1-\dfrac{1}{3}\right).\left(1-\dfrac{1}{4}\right)....\left(1-\dfrac{1}{20}\right)\)
