\(a,=\dfrac{5}{6}+\dfrac{6}{7}\\ =\dfrac{35}{42}+\dfrac{36}{42}=\dfrac{71}{42}\\ b,=\dfrac{5}{6}+\dfrac{4}{9}\\ =\dfrac{15}{18}+\dfrac{8}{18}=\dfrac{23}{18}\)

21/10

17/4

a) 6/1x 2/5-3/10

= 12/5- 3/10

= 21/10

b) (4/6+5):4/3

= 17/3x 3/4

= 17/4

a) 6 : 5/2 - 3/10 = 12/5 - 3/10 = 21/10

b) 4/6 : 4/3 + 5 : 4/3 = 1/2 + 5 : 4/3 = 1/2 + 15 /4 = 17/4

a)

`6:5/2-3/10`

`=6xx2/5-3/10`

`=12/5-3/10`

`=24/10-3/10`

`=21/10`

b)

`4/6:4/3+5:4/3`

`=2/3xx3/4+5xx3/4`

`=3/4xx(2/3+5)`

`=3/4xx(2/3+15/3)`

`=3/4xx17/3`

`=17/4`

\(a,6:\dfrac{5}{2}-\dfrac{3}{10}\\ =\dfrac{6}{1}:\dfrac{5}{2}-\dfrac{3}{10}\\ =\dfrac{6}{1}\times\dfrac{5}{2}-\dfrac{3}{10}\\ =\dfrac{12}{5}-\dfrac{3}{10}\\ =\dfrac{12\times2}{5\times2}-\dfrac{3}{10}\\ =\dfrac{24}{10}-\dfrac{3}{10}\\ =\dfrac{21}{10}\) 

\(b,\dfrac{4}{6}:\dfrac{4}{3}+5:\dfrac{4}{3}\\ =\dfrac{4}{6}:\dfrac{4}{3}+\dfrac{5}{1}:\dfrac{4}{3}\\ =\dfrac{4}{3}:\left(\dfrac{4}{6}+\dfrac{5}{1}\right)\\ =\dfrac{4}{3}:\left(\dfrac{4}{6}+\dfrac{5\times6}{1\times6}\right)\\ =\dfrac{4}{3}:\left(\dfrac{4}{6}+\dfrac{30}{6}\right)\\ =\dfrac{4}{3}:\dfrac{34}{6}\\ =\dfrac{4}{3}:\dfrac{17}{3}\\ =\dfrac{4}{3}\times\dfrac{3}{17}\\=\dfrac{12}{51} \\ =\dfrac{4}{17}.\)

\(a,6:\dfrac{5}{2}-\dfrac{3}{10}=6\times\dfrac{5}{2}-\dfrac{3}{10}=\dfrac{12}{5}-\dfrac{3}{10}=\dfrac{24}{10}-\dfrac{3}{10}=\dfrac{21}{10}\)

\(b,\dfrac{4}{6}:\dfrac{4}{3}+5:\dfrac{4}{3}=\dfrac{4}{6}\times\dfrac{3}{4}+5\times\dfrac{3}{4}=\dfrac{2}{4}+\dfrac{15}{4}=\dfrac{17}{4}\)

a) \(27+86-\left(29-5+84\right)\)

\(=27+86-29+5-84\)

\(=2+5-2\)

=5

b) \(39-\left(298-89\right)+299\)

\(=39-298+89+299\)

\(=129\)

Tính giá trị của biểu thức:

a) (27 + 86) - (29 - 5 + 84);

=  27 + 86 – 29 + 5 - 84

= 5

b) 39 - (298 - 89) + 299.

= 39 – 298 + 89 + 299

= 129

a) (27 + 86) - (29 - 5 + 84) 

= 27 + 86 - 29 + 5 - 84 

= (27 – 29) + (86 – 84) + 5

= (- 2) + 2 + 5

= 0 + 5

= 5

b) 39 - (298 - 89) + 299 

= 39 - 298 + 89 + 299

= (39 + 89) + (299 – 298)

= 39 + 89 + 1

= 39 + (89 + 1)

= 39 + 90

= 129

a) (-12). (7 - 72) - 25. (55 - 43) 

= (-12). (- 65) - 25. 12 

= 12. 65 – 12. 25

= 12. (65 - 25) 

= 12. 40 

= 480

b) (39 - 19) : (- 2) + (34 - 22). 5 

= 20 : (- 2) + 12. 5 

= - 10 + 60

= 60 - 10 

= 50.

\(2\cdot\left|-21\right|-3\cdot\left|125\right|-5\cdot\left|-33\right|-\left|2\cdot21\right|\)

\(=2\cdot21-3\cdot125-5\cdot33-2\cdot21\)

\(=-3\cdot125-5\cdot33=-375-165=-540\)

\(A=\dfrac{7}{3}+\dfrac{5}{7}+\dfrac{2}{3}-\dfrac{7}{12}+\dfrac{5}{2}=3+\dfrac{221}{84}=\dfrac{473}{84}\)

a,A =  x² - x + 5 ,khi x = 2

= 2² - 2 + 5

= 7.

a: Thay x=2 vào A, ta được:

\(A=2^2-2+5=4+5-2=7\)