S = \(\dfrac{-1}{1.2}\) - \(\dfrac{1}{2.3}\) - \(\dfrac{1}{3.4}\) - - - \(\dfrac{1}{\left(n-1\right).n}\) ( tính)
help yourself with home !!!!!!!!!!!!
Ta có:
\(S=\dfrac{-1}{1.2}-\dfrac{1}{2.3}-\dfrac{1}{3.4}-...-\dfrac{1}{\left(n-1\right)n}\\ S=-\left(\dfrac{1}{1.2}+\dfrac{1}{2.3}+\dfrac{1}{3.4}+...+\dfrac{1}{\left(n-1\right)n}\right)\\ S=-\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{n-1}-\dfrac{1}{n}\right)\\ S=-\left(1-\dfrac{1}{n}\right)\\ S=-\dfrac{n-1}{n}\)
Vậy \(S=-\dfrac{n-1}{n}\)
( 3-1/4 + 2/3 ) - ( 5 + 1/3 - 6/5 ) - ( 6- 7/4 - 3/2 )
A = ( 6 - \(\dfrac{2}{3}\) + \(\dfrac{1}{2}\)) - ( 5 + \(\dfrac{5}{3}\) - \(\dfrac{3}{2}\)) - (3 - \(\dfrac{7}{3}\) + \(\dfrac{5}{2}\))
tính nhanh :
a,\(\dfrac{4}{3}\) - [(\(\dfrac{-11}{6}\) )- (\(\dfrac{2}{9}\) + \(\dfrac{5}{3}\))]
b, (8- \(\dfrac{9}{4}\) +\(\dfrac{2}{7}\) ) - ( -6 -\(\dfrac{3}{7}\) +\(\dfrac{5}{4}\) ) - ( 3+ \(\dfrac{2}{4}\) - \(\dfrac{9}{7}\) )
x-3=5-x
Tìm x biết: (x-3)^2-x|x-3|=0
tim a b \(\in Q\)
a, a - b = 2 \(\left(a+b\right)=a\div b\)
b, a + b = a . b = a \(\div\) b
giup minh nhe minh dang can gap
mẫu chung của 9;6;4
tìm x biết :
\(\dfrac{-4}{7}-x=\dfrac{3}{5}-2\cdot x\)
giúp mk nha 5h đi học rùi
\(\left(\dfrac{1}{2}.x-\dfrac{2}{3}\right)-\left(\dfrac{1}{3}.x-1\right)=\left(x-3\right)-\left(x-1\right)\)
\(\dfrac{x+1}{x+2}=\dfrac{0,8}{1,2}\)
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