Sửa:

\(=4x^2-\dfrac{4}{9}\)

\(\left(2x-\dfrac{2}{3}\right)\cdot\left(\dfrac{2}{3}+2x\right)\\ =2x\cdot\dfrac{2}{3}+2x\cdot2x-\dfrac{2}{3}\cdot\dfrac{2}{3}-\dfrac{2}{3}\cdot2x\\ =\dfrac{4x}{3}+4x-\dfrac{4}{9}-\dfrac{4x}{3}\\ =4x-\dfrac{4}{9}\)

Sửa: 

\(\Rightarrow3x=6\\ \Rightarrow x=6:3\\ \Rightarrow x=2\)

\(\left(3x+1\right)^3:7=49\\ \Rightarrow\left(3x+1\right)^3=49\cdot7\\ \Rightarrow\left(3x+1\right)^3=343\\ \Rightarrow\left(3x+1\right)^3=7^3\\ \Rightarrow3x+1=7\\ \Rightarrow3x=6\\ \Rightarrow x=6:2\\ \Rightarrow x=3\)

Cậu xem lại bài: \(\dfrac{1}{2023\times2025}\) hay \(\dfrac{1}{2023\times2024}\) ạ

\(\left(x+1\right)\left(x-1\right)-\left(x+1\right)\\ =x^2-1^2-x-1\\ =x^2-1-x-1\\ =x^2-x-2\)

\(0,6\times7+1,2\times54+1,8\\ =0,6\times7+0,6\times2\times54+0,6\times3\\ =0,6\times\left(7+2\times54+3\right)\\ =0,6\times\left(7+108+3\right)\\ =0,6\times118\\ =70,8\)

\(1,2\times15+1,2\times74+1,2\\ =1,2\times\left(15+74+1\right)\\ =1,2\times90=108\)

\(1,2\times15+1,2\times74+1,2\\ =1,2\times\left(15+74+1\right)\\ =12\times100\\ =1200\)

Sửa đề: 

\(\dfrac{15}{23}-\dfrac{21}{23}-\left(-\dfrac{8}{23}\right)-\left(-\dfrac{21}{23}\right)\\ =\dfrac{15}{23}-\dfrac{21}{23}+\dfrac{8}{23}+\dfrac{21}{23}\\ =\left(\dfrac{15}{23}+\dfrac{8}{23}\right)+\left(-\dfrac{21}{23}+\dfrac{21}{23}\right)\\ =1+0\\ =1\)