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a)\(-\dfrac{2}{5}.\dfrac{4}{7}+\dfrac{-3}{5}.\dfrac{2}{7}+\dfrac{-3}{5}\)
=\(-\dfrac{2}{5}.\dfrac{4}{7}+\dfrac{3}{7}.\dfrac{-2}{5}+\dfrac{-3}{5}\)
=\(-\dfrac{2}{5}.\left(\dfrac{4}{7}+\dfrac{3}{7}\right)+\dfrac{-3}{5}\)
=\(\dfrac{-2}{5}.1+\dfrac{-3}{5}\)
=\(-\dfrac{2}{5}+\dfrac{-3}{5}\)
=\(-\dfrac{5}{5}\) = -1
\(\dfrac{5}{9}.\dfrac{14}{17}+\dfrac{1}{17}.\dfrac{5}{9}+\dfrac{2}{9}+\dfrac{5}{12}\)
=\(\dfrac{5}{9}.\left(\dfrac{14}{17}+\dfrac{1}{17}\right)+\dfrac{2}{9}+\dfrac{5}{12}\)
=\(\dfrac{5}{9}.\dfrac{15}{17}+\dfrac{2}{9}+\dfrac{5}{12}\)
=\(\dfrac{25}{51}+\dfrac{2}{9}+\dfrac{5}{12}\)
=\(\dfrac{691}{612}\)
a)4*x+79*29=79*33
4*x+2291=2607
4*x=2607-2291=316
x=316:4=79
b)83-3*(7+x)=64
3*(7+x)=83- 64=19
7+x=19:3=19/3
x=19/3-7=-2/3
117:{[79-3(3^3 -17)]:7+2}
=117:{[79-3(27-17)]:7+2}
=117:{[79-3.10]:7+2}
=117:{[79-30]:7+2}
=117:{49:7+2}
=117:{7+2}
=117:9
=13
\(\frac{17}{33}.\frac{2}{5}+\frac{3}{5}.\frac{17}{33}-\frac{17}{33}\)
\(=\frac{17}{33}\times\frac{2}{5}+\frac{3}{5}\times\frac{17}{33}-\frac{17}{33}\times1\)
\(=\frac{17}{33}\times\left(\frac{2}{5}+\frac{3}{5}-1\right)\)
\(=\frac{17}{33}\times\left(1-1\right)\)
\(=\frac{17}{33}\times0=\frac{17}{33}\)
+) \(176+483+24+117\)
\(=\left(176+24\right)+\left(483+117\right)\)
\(=200+600\)
\(=800\)
+) \(239+518+761+482\)
\(=\left(239+761\right)+\left(518+482\right)\)
\(=1000+1000\)
\(=2000\)
+) \(32+33+34+...+78+79+80\)
Số số hạng của dãy là :
\(\left(80-32\right):1+1=49\) (số)
Tổng của dãy là :
\(\frac{\left(80+32\right)\times49}{2}=2744\)
+) \(5\times125\times2\times4\)
\(=\left(5\times2\right)\times\left(125\times4\right)\)
\(=10\times500\)
\(=5000\)
+) \(25\times50\times4\times20\)
\(=\left(25\times4\right)\times\left(50\times20\right)\)
\(=100\times1000\)
\(=100000\)
+) \(17\times32+43\times17+17\times25\)
\(=17\times\left(32+43+25\right)\)
\(=17\times100\)
\(=1700\)
+) \(24\times19+29\times24+18\times24+24\times33+24\)
\(=24\times\left(19+29+18+33+1\right)\)
\(=24\times100\)
\(=2400\)
_Chúc bạn học tốt_
a)=\(\frac{-2.4}{5.7}+\frac{-3.2}{5.7}+\frac{-3}{5}\)
=\(\frac{-2.4}{5.7}+\frac{-2.3}{5.7}+\frac{-3}{5}\)
=\(\frac{-2}{5}\left(\frac{4+3}{7}\right)+\frac{-3}{5}\)
=\(\frac{-2}{5}.1+\frac{-3}{5}\)
=-1
b)
\(=117:\left[\left(79-3\cdot16\right):7+2\right]=117:\left[\left(79-48\right):7+2\right]\)
=117/5
117:{[79-3(33 -17)]:7+2}
=117:{[79-3.16]:7+2}
=117:{[79-48]:7+2}
=117:{31:7+2}
=117:{\(\dfrac{31}{7}\)+2}
=117:\(\dfrac{45}{7}\)
=\(\dfrac{91}{5}\)