Ta có: \(\frac{2022}{2021}\times\frac54-\frac{1}{2021}\times\frac54\)

\(=\frac54\times\left(\frac{2022}{2021}-\frac{1}{2021}\right)\)

\(=\frac54\times\frac{2021}{2021}=\frac54\)

Tìm x ∈ N

a) 2x chia hết cho 12 ⇒ 2x ∈ B(12) 

2x chia hết cho 30 ⇒ 2x ∈ B(30) 

Mà x có hai chữ số ⇒ 10 ≤ x ≤ 99 

\(\Rightarrow2x\in BC\left(12;30\right)\)

Mà: \(B\left(12\right)=\left\{0;12;24;36;48;60;72;84;96;108;...\right\}\)

\(B\left(30\right)=\left\{0;30;60;90;120;...\right\}\)

\(\Rightarrow BC\left(12;30\right)=\left\{0;60;...\right\}\)

\(\Rightarrow2x=60\)

\(\Rightarrow x=\dfrac{60}{2}\\ \Rightarrow x=30\)

b) \(9^{x+2}-9^{x+1}+9^x=657\)

\(\Rightarrow9^x\cdot\left(9^2-9+1\right)=957\)

\(\Rightarrow9^x\cdot\left(81-8\right)=657\)

\(\Rightarrow9^x\cdot73=657\)

\(\Rightarrow9^x=9\)

\(\Rightarrow9^x=9^1\)

\(\Rightarrow x=1\)

bạn có thể giải giùm mk bài tính nhanh đc ko??? Mk đang cần gấp á. Cảm ơn bạn nhiều nha!

\(\frac{1978\cdot1979+1980\cdot21+1958}{1980\cdot1979-1978\cdot1979}=\frac{1978\cdot1979+\left(1979+1\right)\cdot21+1958}{1979\cdot\left(1980-1978\right)}\)

\(=\frac{1978\cdot1979+1979\cdot21+21+1958}{1979\cdot2}=\frac{1979\cdot\left(1978+21+1\right)}{1979\cdot2}=\frac{2000}{2}=1000\)

a, 2009
b, -56

1000 đó bạn ơi chuẩn 10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000%luôn đó bạn

1000 đó bạn 

nguyễn trung hiếu bấm máy chứ gì 

Ta có: \(1978\times1979+21\times1980+1958\)

\(=1978\times\left(1978+1\right)+21\times\left(1978+2\right)+1958\)

\(=1978\times1978+1978+21\times1978+42+1958\)

=1978x1978+21x1978+1978+42+1958

=1978x(1978+21)+1978+2000

=1978x1999+3978

=(1979-1)x(1979+20)+3978

=1979x1979+19x1979-20+3978

=1979x1979+19x1979+3958

=1979x(1979+19+2)

=1979x2000

Ta có: 1980x1979-1978x1979

=1979x(1980-1978)=1979x2

Ta có: \(\frac{1978\times1979+21\times1980+1958}{1980\times1979-1978\times1979}\)

\(=\frac{1979\times2000}{1979\times2}=\frac{2000}{2}=1000\)

1980*1979-1978*1979

=1979*(1980-1978)

=1979*2

=3957

1980x1979-1978x1979

= 1979x(1980-1978)

= 1979x2

= 3957