\(\left(\dfrac{6}{11}+\dfrac{5}{11}\right)\times\dfrac{3}{7}=\dfrac{11}{11}\times\dfrac{3}{7}=1\times\dfrac{3}{7}=\dfrac{3}{7}\)

\(\dfrac{3}{5}\left(\dfrac{7}{9}-\dfrac{2}{9}\right)=\dfrac{3}{5}\times\dfrac{5}{9}=\dfrac{1}{3}\)

`( 6 / 11 + 5 / 11 ) xx 3 / 7 = 11 / 11 xx 3 / 7 = 1 xx 3 / 7 = 3 / 7`

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`3 / 5 xx 7 / 9 - 3 / 5 xx 2 / 9 = 3 / 5 xx ( 7 / 9 - 2 / 9 ) = 3 / 5 xx 5 / 9 = 1 / 3`

Dấu :  \("."\)là dấu nhân nhé 

\(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{77.79}\)

\(=1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{77}-\frac{1}{79}\)

\(=1-\frac{1}{79}\)

\(=\frac{79}{79}-\frac{1}{79}\)

\(=\frac{78}{79}\)

Chúc bạn học tốt !!! 

Giá trị biểu thức là 78/79

[(195+35/7)/8+195]*2-400

=[(195+5)/8+195]*2-400

=[200/8+195]*2-400

=[25+195]*2-400

=220*2-400

=440-400

=40

8/35+2/7:2/4.

=8/35+2/7*4/2.

=8/35+4/7.

=8/35+20/35.

=28/35.

=4/5.

=8/35+2/7x2

=8/35x4/7

=32/245

Ba biểu thức: 4 x 3 – 2; 15 + 2 – 10; 30 – 25 : 5.

= 1-1/3 + 1/3-1/5+.......+1/97-1/99

=  1 - 1/99

= 98/99

sao lại là 1- 1/3 + 1/3 -1/5 + ...... 1/97 - 1/99 hả bạn :|

Theo đề, ta có: \(\frac{2x-3}{35}+\frac{x\left(x-2\right)}{7}\le\frac{5x^2-2}{35}-\frac{2x-3}{5}\)

=>2x-3+5x(x-2)<=\(5x^2-2\) -7(2x-3)

=>\(2x-3+5x^2-10x\le5x^2-2-14x+21\)

=>-8x-3<=-14x+19

=>6x<=22

=>x<=22/6=11/3

3333555555

3333555555 nhé

a. 2205 - (35 . 7)

= 2205 - 245

= 1960

b. 8700 : 25 . 4

= 348 . 4

= 1392

thanks