\(A=2020\cdot2018-2019^2\)

\(\Leftrightarrow A=\left(2019+1\right)\left(2019-1\right)-2019^2\)

\(\Leftrightarrow A=2019^2-1-2019^2\)

\(\Leftrightarrow A=-1\)

À, cái này là dùng hằng đẳng thức của lớp 8 á ^^

Học tốt!!!

#Bo

\(\frac{-1}{3}:\frac{-5}{6}=\frac{-1}{3}\times\frac{-6}{5}=\frac{2}{5}\)

@muối

(-1/3) : (-5/6) = 2/5

\(a,=73.\left(34+1+65\right)=73.100=7300\\ b,=-\left(45+35\right)=-80\\ c,=299-6\left(14:5-3\right)=299-6\left(-\dfrac{1}{5}\right)=299+\dfrac{6}{5}=\dfrac{1501}{5}\)

a: =-(3,54+4,783)=-8,323

b: =23-10=13

c: Sửađề: (-2,86)*4,2-3,14*4,2-6*32

=4,2(-2,86-3,14)-192

=-4,2*6-192

=-25,2-192

=-217,2

a: -3,54-4,783

=-(3,54+4,783)

=-8,323

b: 12,5+(-5,2)+10,5+(-4,8)

=(12,5+10,5)-(5,2+4,8)

=23-10

=13

c:Sửa đề: \(\left(-2,86\right)\cdot42-3,14\cdot42-6\cdot32\)

=\(42\left(-2,86-3,14\right)-6\cdot32\)

\(=42\cdot\left(-6\right)-6\cdot32=-6\left(42+32\right)=-6\cdot74=-444\)

c: \(=5+\dfrac{6}{7}-2-\dfrac{3}{8}-1-\dfrac{1}{8}=2+\dfrac{6}{7}-\dfrac{1}{2}=\dfrac{3}{2}+\dfrac{6}{7}=\dfrac{33}{14}\)

e: \(=\dfrac{-3}{5}\left(-\dfrac{1}{9}-\dfrac{5}{6}+\dfrac{5}{2}\right)=\dfrac{-3}{5}\cdot\dfrac{14}{9}=\dfrac{-14}{15}\)

\(112\cdot35+112\cdot65+800\)

\(=112\cdot\left(35+65\right)+800\)

\(=112\cdot100+800\)

\(=11200+800\)

\(=12000\)