1 - 2 + 3 - 4 +...+ 199 - 200

=( 1 - 2 ) + ( 3 - 4 ) +...........+ ( 199 - 200 )

= -1 + -1 + -1........+ -1 ( 100 lần -1 )

= -100

~ Hok tốt ~

trả lời

<=> (1+1+..+1)x=200

       50 số 1

<=50x=200

<=>x=4

\(\frac{5}{12}.\left(\frac{-3}{4}\right)-\frac{7}{12}.\frac{3}{4}\)

\(=\left(\frac{-5}{12}-\frac{7}{12}\right).\frac{3}{4}\)

\(=\left(-1\right).\frac{3}{4}=\frac{-3}{4}\)

~ Hok tốt ~

\(\frac{5}{12}.\left(-\frac{3}{4}\right)-\frac{7}{12}.\frac{3}{4}\)

\(=\frac{3}{4}.\left(-\frac{5}{12}-\frac{7}{12}\right)\)

\(=\frac{3}{4}.\left(-1\right)\)

\(=-\frac{3}{4}\)

1-2+3-4+5-6+7-8+...+2017-2018

=-1+-1+-1+...+-1

= -1. 1009

= -1009

#)Giải :

\(1-2+3-4+5-6+...+2017-2018\)

\(=\left(1-2\right)+\left(3-4\right)+\left(5-6\right)+...+\left(2017-2018\right)\)( 1009 cặp )

\(=\left(-1\right)+\left(-1\right)+\left(-1\right)+...+\left(-1\right)\)( 1009 chữ số - 1 )

\(=\left(-1\right).1009\)

\(=-1009\)

\(\left(\frac{11}{12}:\frac{33}{16}\right).\frac{3}{5}\)

\(=\frac{11}{12}.\frac{16}{33}.\frac{3}{5}\)

\(=\frac{11.16.3}{12.33.5}\)

\(=\frac{11.4.4.3}{4.3.3.11.5}\)

\(=\frac{4}{15}\)

\(\left(\frac{11}{12}:\frac{33}{16}\right).\frac{3}{5}\)
\(\left(\frac{11}{12}.\frac{16}{33}\right).\frac{3}{5}\)
\(\frac{11}{12}.\frac{16}{33}.\frac{3}{5}=\frac{11.16.3}{12.33.5}=\frac{16}{4.3.5}=\frac{4}{3.5}=\frac{4}{15}\)

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\(\left(-2\right).\left(\frac{-38}{21}\right).\left(\frac{-7}{4}\right).\left(\frac{3}{-8}\right)\)

\(=\frac{\left(-2\right).\left(-38\right).\left(-7\right).\left(-3\right)}{21.4.8}\)

\(=\frac{19}{8}\)

\(\left(-2\right)\cdot\frac{-38}{21}\cdot\frac{-7}{4}\cdot\left(\frac{-3}{8}\right)\)

\(=\frac{-2\cdot\left(-38\right)\cdot\left(-7\right)\cdot\left(-3\right)}{21\cdot4\cdot8}=\frac{-2\cdot\left(-38\right)\cdot21}{21\cdot4\cdot8}=\frac{-2\cdot\left(-38\right)}{32}=\frac{19}{8}\)