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Lời giải:
a.
$(-6)+|83|-(-75)+|-37|=-6+83+75+37=-6+195=195-6=189$
b.
$(-12)-(-26)-[(-9)-|21|)=-12+26-(-9-21)=-12+26+(9+21)$
$=-12+26+30=-12+56=56-12=44$
c.
$15-(-48)-15+(-17)-|-48|=15+48-15-17-48$
$=(15-15)+(48-48)-17=-17$
d.
$-24-(-33)+|24|-(-|78|)-|33|-78$
$=-24+33+24+78-33-78$
$=(-24+24)+(33-33)+(78-78)=0$
\(A=\dfrac{7}{19}\times\dfrac{8}{11}+\dfrac{7}{19}\times\dfrac{3}{11}+\dfrac{12}{19}\)
\(=\dfrac{7}{19}\left(\dfrac{8}{11}+\dfrac{3}{11}\right)+\dfrac{12}{19}\)
\(=\dfrac{7}{19}+\dfrac{12}{19}=\dfrac{19}{19}=1\)
a: \(A=\dfrac{7}{19}\left(\dfrac{8}{11}+\dfrac{3}{11}\right)+\dfrac{12}{19}=\dfrac{7}{19}+\dfrac{12}{19}=1\)
b: \(B=\left(\dfrac{67}{111}+\dfrac{2}{33}-\dfrac{5}{117}\right)\cdot\dfrac{4-3-1}{12}=0\)
S= 1+(-2)+3+(-4)+........(-2014)+2015
S= (-1) + ( -1) +...+(-1)
S= (-1).2015
S= -2015
S= 1+(-2)+3+(-4)+........(-2014)+2015
S=(-1)+(-1)+.......(-1)+2015
S=(-1)x2015+2015
S=(-2015)+2015=0
\(7x-30=2x-5\)
\(\Leftrightarrow7x=2x-5+30\)
\(\Leftrightarrow7x=2x+25\)
\(\Leftrightarrow7x-2x=25\)
\(\Leftrightarrow5x=25\)
\(\Leftrightarrow x=5\)
Vậy \(x=5\)
A=\(\frac{1.2.3.4...49}{2.3.4.5.....50}\)=\(\frac{1}{50}\)
\(A = (1 - \frac{1}{2})(1 - \frac{1}{3})(1 - \frac{1}{4})...(1 - \frac{1}{50})= \frac{1}{2}.\frac{2}{3}.\frac{3}{4}...\frac{49}{50}= \frac{1}{50} \)
\(B = \frac{2^2}{1.3}.\frac{3^2}{2.4}.\frac{4^2}{3.5}.\frac{5^2}{4.6}.\frac{6^2}{5.7}=\frac{2.2}{1.3}.\frac{3.3}{2.4}.\frac{4.4}{3.5}.\frac{5.5}{4.6}.\frac{6.6}{5.7}=\frac{2.3.4.5.6}{1.2.3.4.5}.\frac{2.3.4.5.6}{3.4.5.6.7}=\frac{6}{1}.\frac{2}{7}=\frac{12}{7}\)