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A=\(\dfrac{-2}{9}\)+\(\dfrac{-3}{4}\)+\(\dfrac{3}{5}\)+\(\dfrac{1}{15}\)+\(\dfrac{1}{57}\)+\(\dfrac{1}{3}\)+\(\dfrac{-1}{36}\)
A=(\(\dfrac{-2}{9}\)+\(\dfrac{-3}{4}\)+\(\dfrac{-1}{36}\))+(\(\dfrac{3}{5}\)+\(\dfrac{1}{15}\)+\(\dfrac{1}{3}\))
A=-1+1=0 B=\(\dfrac{1}{2}\)+\(\dfrac{-1}{5}\)+\(\dfrac{-5}{7}\)+\(\dfrac{1}{6}\)+\(\dfrac{-3}{35}\)+\(\dfrac{1}{3}\)+\(\dfrac{1}{41}\) B=(\(\dfrac{-1}{5}\)+\(\dfrac{-5}{7}\)+\(\dfrac{-3}{35}\))+(\(\dfrac{1}{2}\)+\(\dfrac{1}{6}\)+\(\dfrac{1}{3}\))+\(\dfrac{1}{41}\) B=-1+1+\(\dfrac{1}{41}\)=\(\dfrac{1}{41}\)
câu 1 : A=-2/9+-3/4+3/5+1/15+1/57+1/3+-1/36
=(-2/9+-3/4+-1/36)+(3/5+1/15+1/3)
Vậy p/s 1/57 đâu bạn ?
![[IMG]](http://i255.photobucket.com/albums/hh140/the_firedragon_24/cuteonion23.gif)
c) Ta có: \(\dfrac{3}{5}+\dfrac{-5}{20}+\dfrac{30}{75}+\dfrac{-7}{4}\)
\(=\dfrac{3}{5}+\dfrac{2}{5}+\dfrac{-1}{4}+\dfrac{-7}{4}\)
\(=1-2=-1\)
Giải:
a)-1/12+4/3=-1/12+16/12=15/12=5/4
b)(-4/14-3/15)-(1/5-20/35-(-1)).7
=-17/35-22/35.7
=-17/35-22/5
=-171/35
c)3/5+-5/20+30/75+-7/4
=3/5+-1/4+2/5+-7/4
=(3/5+2/5)+(-1/4+-7/4)
=1+-2
=-1
d)5/6.-12/14+7/13
=-5/7+7/13
=-16/91
e)2/-9-5/-36-1/4
=-1/12-1/4
=-1/3
f)2/23+-5/12+7/18+21/23+-7/12
=(2/23+21/23)+(-5/12+-7/12)+7/18
=1+-1+7/18
=7/18
\(\dfrac{-2}{9}-\dfrac{3}{4}+\dfrac{3}{5}+\dfrac{1}{15}+\dfrac{1}{57}+\dfrac{1}{3}-\dfrac{1}{36}\)
\(=\left(-\dfrac{2}{9}-\dfrac{3}{4}-\dfrac{1}{36}\right)+\left(\dfrac{3}{5}+\dfrac{1}{15}+\dfrac{1}{3}\right)+\dfrac{1}{57}\)
\(=\dfrac{-8-27-1}{36}+\dfrac{9+1+5}{15}+\dfrac{1}{57}\)
\(=-\dfrac{36}{36}+\dfrac{15}{15}+\dfrac{1}{57}\)
\(=\dfrac{1}{57}\)