a) \(\left|-\frac{6}{7}\right|\div\left(-2\right)^3-\sqrt{\frac{9}{16}}\)

\(=\frac{6}{7}\div\left(-8\right)-\frac{3}{4}\)

\(=\frac{-3}{28}-\frac{3}{4}\)

\(=\frac{-6}{7}\)

b) \(-5\frac{5}{9}\div\left(-1\frac{3}{4}\right)+4\frac{5}{9}\div\left(-1\frac{3}{4}\right)\)

\(=\left(-5\frac{5}{9}+4\frac{5}{9}\right)\div\left(-1\frac{3}{4}\right)\)

\(=\left(-5+\frac{5}{9}+4+\frac{5}{9}\right)\div\frac{-7}{4}\)

\(=\left(-1+\frac{10}{9}\right).\frac{-4}{7}\)

\(=\frac{1}{9}.\frac{-4}{7}\)

\(=\frac{-4}{63}\)

c) \(-63,99-\left(\frac{4}{9}-63,99\right)-\left(-1\frac{2}{3}\right)^2\)

\(=-63,99-\frac{4}{9}+63,99-\left(\frac{-5}{3}\right)^2\)

\(=-63,99-\frac{4}{9}+63,99-\frac{25}{9}\)

\(=\left(-63,99+63,99\right)-\left(\frac{4}{9}+\frac{25}{9}\right)\)

\(=-\frac{29}{9}\)

giúp tớ với

Câu 1: 

a) \(=\frac{42}{5}:\frac{14}{5}\)

\(=3\)

b)

 \(=15-\frac{7}{3}:\left(\frac{4}{9}-\frac{1}{6}\right)\)

\(=15-\frac{7}{3}:\frac{4}{9}+\frac{7}{3}:\frac{1}{6}\)

\(=15-\frac{21}{4}+14\)

\(=29-\frac{21}{4}=29-5-\frac{1}{4}\)

\(=24-\frac{1}{4}=\frac{95}{4}\)

\(\left(\frac{1}{4}-x\right)\left(x+\frac{2}{5}\right)=0\)

Ta xét 2 trường hợp 

\(\begin{cases}\frac{1}{4}-x=0\\x+\frac{2}{5}=0\end{cases}\Rightarrow\orbr{\begin{cases}x=\frac{1}{4}\\x=-\frac{2}{5}\end{cases}}\)

tớ mới làm bài 1 thôi bài 2 3 tớ ko có thời gian 

Bài 1: Tìm x, biết:

\(\left(\frac{1}{4}-x\right)\left(x+\frac{2}{5}\right)=0\)

\(\Rightarrow\hept{\begin{cases}\frac{1}{4}-x=0\\x+\frac{2}{5}=0\end{cases}\Rightarrow\hept{\begin{cases}x=\frac{1}{4}\\x=-\frac{2}{5}\end{cases}}}\)

c)  C = ( 1 - 2 ) + ( 3 - 4 ) + ... + ( 79 - 80 )

     C = ( -1 ) + ( -1 ) + ... + ( -1 )

     C = ( -1 ) x ( 80 - 1 + 1 ) : 2

     C = ( -1 ) x 80 : 2

     C = ( -40 )

C=1-2+3-4+...+79-80

=(1-2)+(3-4)+...+(79-80)

=-1+(-1)+...+(-1) (có 80 số hạng bàng -1)

=-1*80

=-80

a) A = \(\frac{15}{7}:\left(\frac{1}{15}-\frac{7}{5}\right)-\frac{15}{7}:\left(\frac{17}{15}+\frac{11}{5}\right)=\frac{15}{7}:\frac{-20}{15}-\frac{15}{7}:\frac{50}{15}\)

A = \(\frac{15}{7}.\frac{15}{-20}-\frac{15}{7}.\frac{15}{50}=\frac{15}{7}.\left(\frac{-15}{20}-\frac{15}{50}\right)=\frac{15}{7}.\frac{-105}{100}=-\frac{9}{4}\)

b) B = \(\frac{1}{\left(-\frac{2}{3}\right)^4}.\left(-4\right)^2-1^{2016}-10\frac{1}{3}=\frac{1}{\frac{16}{81}}.16-1-10\frac{1}{3}=\frac{81}{16}.16-1-10\frac{1}{3}\)

B = \(81-1-10-\frac{1}{3}=70-\frac{1}{3}=\frac{209}{3}\)

= [ 60/90 - ( 12/15 + 10/15) ] : 6/5

= ( 2/3 - 22/15 ) x 5/6

= ( 10/15 - 22/15 ) x 5/6

= -12/15 x 5/6

= -60/90

= -2/3

( 15/10 x 4/9 - ( 4/5 + 2/3 )) : 6/5

( 15/10 x 4/9 - ( 12/15 + 10/15 )) : 6/5

(30/45 - 66/45 ) : 6/5

-12/15 : 6/5 ( đã rút gọn -36/45 = -12/15 )

-2/3

k mk na <3

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