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1+2+3+4+5+6+7+8+9+10=55
11+12+13+14+15+16+17+18+19+20=155
1+2+3+4+5+6+7+8+9+10+11+12+13+14 +15+16+17+18+19+20+21+22+23+24+25+26+27+28+29+30-50-53=362
a; - \(\dfrac{10}{13}\) + \(\dfrac{5}{17}\) - \(\dfrac{3}{13}\) + \(\dfrac{12}{17}\) - \(\dfrac{11}{20}\)
= - (\(\dfrac{10}{13}\) + \(\dfrac{3}{13}\)) + (\(\dfrac{5}{17}\) + \(\dfrac{12}{17}\)) - \(\dfrac{11}{20}\)
= - 1 + 1 - \(\dfrac{11}{20}\)
= 0 - \(\dfrac{11}{20}\)
= - \(\dfrac{11}{20}\)
b; \(\dfrac{3}{4}\) + \(\dfrac{-5}{6}\) - \(\dfrac{11}{-12}\)
= \(\dfrac{9}{12}\) - \(\dfrac{10}{12}\) + \(\dfrac{11}{12}\)
= \(\dfrac{10}{12}\)
= \(\dfrac{5}{6}\)
c; [13.\(\dfrac{4}{9}\) + 2.\(\dfrac{1}{9}\)] - 3.\(\dfrac{4}{9}\)
= [\(\dfrac{52}{9}\) + \(\dfrac{2}{9}\)] - \(\dfrac{4}{3}\)
= \(\dfrac{54}{9}\) - \(\dfrac{4}{3}\)
= \(\dfrac{14}{3}\)
\(1+2+3+4+5+6+7+8+9+10=55\)
\(11+12+13+14+15+16+17+18+19+20=155\)
Câu 1:
(\(\frac{3x}{7}\)\(+\)\(1\))\(\div\)(\(-4\)) \(=-\)\(\frac{1}{28}\)
\(\Leftrightarrow\)\(\frac{3x}{7}\)\(+\)\(1=-\)\(\frac{1}{28}\)\(\times\)(\(-4\))
\(\Leftrightarrow\)\(\frac{3x}{7}\)\(+\)\(1=\)\(\frac{1}{7}\)
\(\Leftrightarrow\)\(\frac{3x}{7}\)\(=\)\(\frac{1}{7}\)\(-1\)
\(\Leftrightarrow\)\(\frac{3x}{7}\)\(=-\)\(\frac{6}{7}\)
\(\Leftrightarrow\)\(x\)\(=-\)\(\frac{6}{7}\)\(\div\)\(\frac{3}{7}\)
\(\Leftrightarrow\)\(x\)\(=\)\(-2\)
\(\left(\frac{3x}{7}+1\right):\left(-4\right)=\frac{-1}{28}\)
\(\frac{3x}{7}+1=\frac{-1}{28}x\left(-4\right)\)
\(\frac{3x}{7}+1=\frac{1}{7}\)
\(\frac{3x}{7}=\frac{1}{7}-1\)
\(\frac{3x}{7}=\frac{-6}{7}\)
=>x=\(\frac{-6}{7}x\frac{7}{3}=-2\)
VẬY X=-2