Bài 11: Nhân hai số nguyên cùng dấu

a: \(\left(-150\right):\left(-5\right)-2\cdot5^2\)

\(=\dfrac{150}{5}-2\cdot25\)

=30-50

=-20

b: \(2040-\left[10\cdot\left(4^3-46\right):18+2^3\right]\cdot2022^0\)

\(=2040-\left[10\cdot\left(64-46\right):18+8\right]\)

\(=2040-\left[10\cdot18:18+8\right]\)

\(=2040-10-8=2030-8=2022\)

a: \(=\dfrac{-3}{4}-\dfrac{1}{36}-\dfrac{2}{9}+\dfrac{1}{3}+\dfrac{1}{15}+\dfrac{3}{5}+\dfrac{1}{57}\)

=1/57-1+1

=1/57

b: \(=\dfrac{1}{4}\left(\dfrac{4}{1\cdot5}+\dfrac{4}{5\cdot9}+...+\dfrac{4}{41\cdot45}\right)\)

\(=\dfrac{1}{4}\left(1-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{9}+...+\dfrac{1}{41}-\dfrac{1}{45}\right)\)

=1/4*44/45

=11/45

\(a,\left(8-x\right)\left(x+5\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}8-x=0\\x+5=0\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=8\\x=-5\end{matrix}\right.\\ b,2x\left(x+81\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}2x=0\\x+81=0\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=0\\x=-81\end{matrix}\right.\)

a)\(\left(8-x\right)\left(x+5\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}8-x=0\\x+5=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=8\\x=-5\end{matrix}\right.\)
b)\(2x\left(x+81\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}2x=0\\x+81=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=0\\x=-81\end{matrix}\right.\)

\(-4.(-125).(-3).(-8)\)

\(=500.(-3).(-8)\)

\(=-1500.(-8)\)

\(=12000\)

=4*125*3*8

=1000*12

=12000

4:

d: =7*3-7*5-9*2+9*7

=7(3-5+9)-18

=7*7-18=49-18=31

e: =23(7-15-5+3)=23*(-10)=-230

tham khảo:Hay nói ngắn gọn: Tích hai số cùng dấu thì dương. Tích hai số khác dấu thì âm.

\(\dfrac{x}{2}=\dfrac{-27}{13}\cdot\dfrac{5}{9}\)

\(\dfrac{x}{2}=-\dfrac{15}{13}\)

\(x=\dfrac{\left(-15\right)\cdot2}{13}\)

\(x=-\dfrac{30}{13}\)

\(=-\dfrac{2}{3}\times\left(\dfrac{5}{17}+\dfrac{12}{17}\right)+\dfrac{5}{13}\)

\(=-\dfrac{2}{3}\times1+\dfrac{5}{13}\)

\(=-\dfrac{26}{39}+\dfrac{15}{39}=-\dfrac{11}{39}\)

\(\dfrac{8}{35}.\dfrac{5}{4}\)

\(\dfrac{2}{7}\)