(1981 x 1982 - 990) : (1980 x 1982 + 992)

=(1980 x 1982+1982 -990) : (1980 x 1982 +992)

=(1980 x 1982 + 992) : ( 1980 x 1982 + 992)

=1

Bạn chờ mình khoảng 2 phút nha1

a)

  \(A=\left(1+2+2^2+2^3+2^4\right)+\left(2^5+2^6+2^7+2^8+2^9\right)+...+\left(2^{96}+2^{97}+...+2^{100}\right)\)

\(A=31+31\cdot2^5+...+31\cdot2^{96}=31\cdot\left(1+2^5+...+2^{96}\right)⋮31\)

b)

\(A=\left(1+2+2^2\right)+\left(2^3+2^4+2^5\right)+...+\left(2^{98}+2^{99}+2^{100}\right)\)

\(A=7+7\cdot2^3+...+7\cdot2^{98}=7\cdot\left(1+2^3+...+2^{98}\right)⋮7\)

a. chia hết cho 6

b. chia hết cho 8

c. chia hết cho 18

d. chia hết cho 12

làm câu d) thui thấy tụi quá

ta có :    a² + a + 1 \(⋮\)a + 1

  =) [  a² + a + 1 - ( a + 1 ) \(⋮\)a + 1

 =) a² \(⋮\)a + 1

=) [ a² - ( a + 1 )] \(⋮\) a + 1

=) [ a² - a( a + 1 )] \(⋮\)a + 1

=) a \(⋮\)a + 1

=) a \(\in\){ 0 : -2 }

\(a,a+5⋮a-1\)

\(=>a-1+6⋮a-1\)

Do \(a-1⋮a-1\)

\(=>6⋮a-1\)

\(=>a-1\inƯ\left(6\right)=\left\{-6;-3;-2;-1;1;2;3;6\right\}\)

\(=>a\in\left\{-5;-2;-1;0;2;3;4;7\right\}\)

\(b,2a⋮a-1\)

\(=>2a-2+2⋮a-1\)

\(=>2.\left(a-1\right)+2⋮a-1\)

\(Do:2.\left(a-1\right)⋮a-1\)

\(=>2⋮a-1\)

\(=>a-1\inƯ\left(-2;-1;1;2\right)\)

\(=>a\in\left\{-1;0;2;3\right\}\)

\(c,3a-8⋮a-4\)

\(=>3.\left(a-4\right)+4⋮a-4\)

\(Do:3.\left(a-4\right)⋮a-4\)

\(=>4⋮a-4\)

\(=>a-4\inƯ\left(4\right)=\left\{-4;-2;-1;1;2;4\right\}\)

\(=>a\in\left\{0;2;3;5;6;8\right\}\)

D thì bạn kia làm rồi