a) \(...-\dfrac{22}{7}:-\dfrac{15}{9}=\dfrac{22}{7}.\dfrac{9}{15}=\dfrac{66}{35}\)

b) \(...\dfrac{8}{3}:\left(-\dfrac{42}{7}\right)=\dfrac{8}{3}.\left(-\dfrac{7}{42}\right)=-\dfrac{8}{9}\)

c) ...\(\left(-\dfrac{7}{2}\right):\left(-\dfrac{13}{5}\right)=\dfrac{7}{2}.\dfrac{5}{13}=\dfrac{35}{36}\)

\(-\dfrac{12}{21}\div\dfrac{34}{43}\)

\(=-\dfrac{12}{21}\times\dfrac{43}{34}\)

\(=-\dfrac{86}{119}\)

\(-\dfrac{12}{21}:\dfrac{34}{43}=-\dfrac{12}{21}.\dfrac{43}{34}=-\dfrac{2}{7}.\dfrac{43}{17}=-\dfrac{86}{119}\)

\(\dfrac{17}{15}\div\dfrac{4}{3}\)

\(=\dfrac{17}{15}\times\dfrac{3}{4}\)

\(=\dfrac{17}{20}\)

\(7^6+7^5-7^4⋮555\)

\(=7^6+7^5-7^4\)

\(=7^{6+5-4}\)

\(=7^7⋮̸555\)

=> Biểu thức trên không chia hết cho 555

\(1,8\div\left(-\dfrac{3}{4}\right)\)

\(=1,8\times-\dfrac{4}{3}\)

\(=-\dfrac{12}{5}\)

a)\(-\dfrac{2}{5}:-\dfrac{3}{4}\\ =-\dfrac{2}{5}\cdot-\dfrac{4}{3}=\dfrac{8}{15}\)

b)\(4\dfrac{1}{5}:\left(-2\dfrac{4}{5}\right)=\dfrac{21}{5}:\left(-\dfrac{14}{5}\right)=-\dfrac{3}{2}\)

Bài 2:

Chu vi hình chữ nhật:

\(\left(4\dfrac{3}{7}+2\dfrac{1}{5}\right).2=\left(\dfrac{31}{7}+\dfrac{11}{5}\right).2=\dfrac{232}{35}.2=\dfrac{464}{35}\left(m\right)\)

Diện tích hình chữ nhật:

\(4\dfrac{3}{7}.2\dfrac{1}{5}=\dfrac{31}{7}.\dfrac{11}{5}=\dfrac{341}{35}\left(m^2\right)\)

Chu vi : \(\left(4+2\right).2=12\left(m\right)\)

\(S=4.2=8\left(m^2\right)\)

giúp mình với

\(2\dfrac{2}{5}\times\dfrac{-3}{4}\)

\(=\dfrac{12}{5}\times\dfrac{-3}{4}\)

\(=-\dfrac{36}{20}\)

\(=-\dfrac{9}{5}\)

\(x^2⋮6\Rightarrow x^2\in\left\{1;2;3;6\right\}\)

\(\Rightarrow x\in\left\{1;\sqrt[]{2};\sqrt[]{3};\sqrt[]{6}\right\}\)

\(\Rightarrow x\in\left\{1\right\}\left(x\in N\right)\)

\(\Rightarrow\forall x\inℕ,x^2⋮6\Rightarrow x⋮6\) là mệnh đề sai

Bạn xem lại nhé, đề viết với mọi x ∈ N mà bạn, bạn mới xét vài trường hợp chứ không bao quát