Câu `12`

\(\)`a, x -2 1/6 =1/3`

`=> x- 13/6 =1/3`

`=>x=1/3+13/6`

`=>x= 2/6 +13/6`

`=>x=15/6`

`b, x+3/4=(-3/2)^8 :(-3/2)^6`

`=> x+3/4=(-3/2)^2`

`=> x+3/4=9/4`

`=>x=9/4-3/4`

`=>x=6/4`

`=>x=3/2`

`c, 1/10 :(3/4-2x)^2=0,4`

`=>  1/10 :(3/4-2x)^2= 2/5`

`=> (3/4-2x)^2=1/10:2/5`

`=> (3/4-2x)^2=1/10 xx 5/2`

`=> (3/4-2x)^2=5/20`

`=> (3/4-2x)^2=1/4`

`=>  (3/4-2x)^2=(+- 1/2)^2`

\(\Rightarrow\left[{}\begin{matrix}\dfrac{3}{4}-2x=\dfrac{1}{2}\\\dfrac{3}{4}-2x=-\dfrac{1}{2}\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}2x=\dfrac{1}{4}\\2x=\dfrac{5}{4}\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=\dfrac{1}{8}\\x=\dfrac{5}{8}\end{matrix}\right.\)

`2448:[119-(x-6)]=24`

`=>119-(x-6)= 2448 : 24`

`=>119-(x-6)= 102`

`=> x-6=119-102`

`=> x-6=17`

`=>x=17+6`

`=>x=23`

c xem lại chứ đúng mà;-;?

Mình xl;-; cậu đổi b thành d, d thành b nha;-;

Câu b theo cách thuận lợi :

\(b,-\dfrac{2}{9}\cdot\dfrac{3}{7}+\dfrac{4}{7}\cdot-\dfrac{2}{9}\\ =-\dfrac{2}{9}\cdot\left(\dfrac{3}{7}+\dfrac{4}{7}\right)\\ =-\dfrac{2}{9}\cdot\dfrac{7}{7}\\ =-\dfrac{2}{9}\cdot1\\ =-\dfrac{2}{9}\)

\(c,\left(\dfrac{10}{7}+\dfrac{11}{6}\right)-\left(\dfrac{3}{7}+\dfrac{5}{6}\right)\\ =\dfrac{10}{7}+\dfrac{11}{6}-\dfrac{3}{7}-\dfrac{5}{6}\\ =\left(\dfrac{10}{7}-\dfrac{3}{7}\right)+\left(\dfrac{11}{6}-\dfrac{5}{6}\right)\\ =\dfrac{7}{7}+\dfrac{6}{6}\\=1+1\\ =2\)

Bài `2`

\(a,\dfrac{3}{8}+\left(\dfrac{1}{2}\right)^5:\left(\dfrac{1}{2}\right)^2\\ =\dfrac{3}{8}+\left(\dfrac{1}{2}\right)^{5-2}\\ =\dfrac{3}{8}+\left(\dfrac{1}{2}\right)^3\\ =\dfrac{3}{8}+\dfrac{1}{8}\\ =\dfrac{4}{8}\\ =\dfrac{1}{2}\\ b,-\dfrac{2}{9}\cdot\dfrac{3}{7}+\dfrac{4}{7}\cdot\left(-\dfrac{2}{9}\right)\\ =-\dfrac{6}{63}+\left(-\dfrac{8}{63}\right)\\ =-\dfrac{14}{63}\\ =-\dfrac{2}{9}\)

\(c,\) Không nhìn rõ ấy.

\(d,-\left(\dfrac{3}{7}+\dfrac{3}{8}\right)-\left(-\dfrac{3}{8}+\dfrac{4}{7}\right)\\ =-\dfrac{3}{7}-\dfrac{3}{8}+\dfrac{3}{8}-\dfrac{4}{7}\\ =\left(-\dfrac{3}{7}-\dfrac{4}{7}\right)+\left(-\dfrac{3}{8}+\dfrac{3}{8}\right)\\ =-\dfrac{7}{7}+0\\ =-1\)

\(d,\dfrac{11}{15}+3\dfrac{8}{17}+\left(\dfrac{4}{15}-2\dfrac{8}{17}\right)\\ =\dfrac{11}{15}+3\dfrac{8}{17}+\dfrac{4}{15}+2\dfrac{8}{17}\\ =\left(\dfrac{11}{15}+\dfrac{4}{15}\right)+\left(3\dfrac{8}{17}+2\dfrac{8}{17}\right)\\ =1+\dfrac{101}{17}\\ =\dfrac{118}{17}\)

\(3:\left(-\dfrac{3}{2}\right)^2+\dfrac{1}{9}\cdot6^2\\ =3:\dfrac{9}{4}+\dfrac{1}{9}\cdot36\\ =3\cdot\dfrac{4}{9}+4\\ =\dfrac{12}{9}+4\\ =\dfrac{16}{3}\)

Bài `3`

`x+2/3=2 1/3`

`=> x+ 2/3 = 7/3`

`=> x= 7/3 -2/3`

`=>x=5/3`

Vậy `x=5/3`