\(A\)=\(2^{16}\)+\(2^{17}\)+\(2^{18}\)+\(2^{20}\)

\(A\)=\(2^{16}\). (\(1\)+\(2\)+\(2^2\)+\(2^4\))

\(A\)=\(2^{16}\). \(23\)

\(Mà\)\(23\)\(Chia\)\(hết\)\(cho\)\(23\)

\(\Rightarrow\)\(A\)Chia hết cho \(23\)

Vậy \(A\)chia hết cho \(23\)

nhanh nha đng cần

hahâhahâhahâhh làm tưcjccjcj nguyễn tập an ăn cút ahaaaa

A=2^2+2^3+...+2^20

a)Vì 2 mũ bao nhiêu cũng thành số chẵn nên A chia hết cho 2

b)A=(2^2+2^3)+(2^4+2^5)+...+(2618+2^19)+2^20

   A=2^2.(2+1)+2^4.(2+1)+...+2^18.(2+1)+2^20

   A=2^2.3+2^4.3+...+2^18.3+2^20

   A=3.(2^2+2^4+...+2^18)+2^20

   A=3.(2^2+2^4+...+2^18)+1048576

   => Vì 1+0+4+8+5+7+6=31 mà 31 không chia hết cho 3 nên tổng trên không chia hết cho 3

c) Tui lười làm quá

Bài 1

a, cm : A = 16⁵ + 2¹⁵ ⋮ 3

    A = 16⁵ + 2¹⁵

   A = (2⁴)⁵ +  2¹⁵

  A  = 2²⁰ + 2¹⁵

 A  =  2¹⁵.(2⁵ + 1)

 A = 2¹⁵. 33 ⋮ 3 (đpcm)

b,cm : B = 8⁸ + 2²⁰ ⋮ 17

    B = (2³)⁸ + 2²⁰ 

    B =  2¹⁶ + 2²⁰

    B = 2¹⁶.(1 + 2⁴)

    B = 2¹⁶. 17 ⋮ 17 (đpcm)

c, cm: C = 1 - 2 + 2² - 2³ + 2⁴ - 2⁵ + 2⁶ -...-2²⁰²¹ + 2²⁰²² : 6 dư 1

C=1+(-2+2²-2³+2⁴- 2⁵+2⁶)+...+(-2²⁰¹⁷+2²⁰¹⁸-2²⁰¹⁹+2²⁰²⁰-2²⁰²¹+2²⁰²²)

C = 1 + 42 +...+ 2²⁰¹⁶.(-2 + 2² - 2³ + 2⁴ - 2⁵ + 2⁶)

C = 1 + 42+...+ 2²⁰¹⁶.42

C = 1 + 42.(2⁰+...+2²⁰¹⁶)

42 ⋮ 6 ⇒ C = 1 + 42.(2⁰+...+2²⁰¹⁶) : 6 dư 1 đpcm

a, \(\overline{aaa}\) \(⋮\) 37

    \(\overline{aaa}\) = a x 111 = a x 3 x 37 ⋮ 37 (đpcm)

b, (\(\overline{ab}\) + \(\overline{ba}\)) ⋮ 11

  \(\overline{ab}\) + \(\overline{ba}\) = \(\overline{a0}\) + b + \(\overline{b0}\) + a = \(\overline{aa}\) + \(\overline{bb}\) = a x 11 + b x 11 = 11 x (a+b)⋮11

\(A=17^{18}-17^{16}\\ =17^{16}\cdot\left(17^2-1\right)\\ =17^{16}\cdot\left(289-1\right)\\ =17^{16}\cdot288\\ =17^{16}\cdot18\cdot16⋮18\)

Vậy \(A⋮18\)

\(B=1+3+3^2+...+3^{11}\)

Ta có: \(52=4\cdot13\)

\(B=1+3+3^2+...+3^{11}\\ =\left(1+3\right)+\left(3^2+3^3\right)+...+\left(3^{10}+3^{11}\right)\\ =1\cdot\left(1+3\right)+3^2\cdot\left(1+3\right)+...+3^{10}\cdot\left(1+3\right)\\ =\left(1+3\right)\cdot\left(1+3^2+...+3^{10}\right)\\ =4\cdot\left(1+3^2+...+3^{10}\right)⋮4\)

Vậy \(B⋮4\)

\(B=1+3+3^2+...+3^{11}\\ =\left(1+3+3^2\right)+\left(3^3+3^4+3^5\right)+...+\left(3^9+3^{10}+3^{11}\right)\\ =1\cdot\left(1+3+3^2\right)+3^3\cdot\left(1+3+3^2\right)+...+3^9\cdot\left(1+3+3^2\right)\\ =\left(1+3+3^2\right)\cdot\left(1+3^3+...+3^9\right)\\ =13\cdot\left(1+3^3+...+3^9\right)⋮13\)

Vậy \(B⋮13\)

Vì \(4\) và \(13\) là hai số nguyên tố cùng nhau nên tao có \(B⋮4\cdot13\Leftrightarrow B⋮52\)

Vậy \(B⋮52\)

\(C=3+3^3+3^5+...3^{31}\)

\(C=3+3^3+3^5+...+3^{31}\\ =\left(3+3^3\right)+\left(3^5+3^7\right)+...+\left(3^{29}+3^{31}\right)\\ =1\cdot\left(3+3^3\right)+3^4\cdot\left(3+3^3\right)+...+3^{28}\cdot\left(3+3^3\right)\\ =\left(3+3^3\right)\cdot\left(1+3^4+...+3^{28}\right)\\ =30\cdot\left(1+3^4+...+3^{28}\right)⋮15\left(\text{vì }30⋮15\right)\)

Vậy \(C⋮15\)

\(D=2+2^2+2^3+...+2^{60}\)

Tao có: \(21=3\cdot7;15=3\cdot5\)

\(D=2+2^2+2^3+...+2^{60}\\ =\left(2+2^2\right)+\left(2^3+2^4\right)+...+\left(2^{59}+2^{60}\right)\\ =2\cdot\left(1+2\right)+2^3\cdot\left(1+2\right)+...+2^{59}\cdot\left(1+2\right)\\ =\left(1+2\right)\cdot\left(2+2^3+...+2^{59}\right)\\ =3\cdot\left(2+2^3+...+2^{59}\right)⋮3\)

Vậy \(D⋮3\)

\(D=2+2^2+2^3+...+2^{60}\\ =\left(2+2^3\right)+\left(2^5+2^7\right)+...+\left(2^{57}+2^{59}\right)+\left(2^2+2^4\right)+...+\left(2^{58}+2^{60}\right)\\ =2\cdot\left(1+2^2\right)+2^5\cdot\left(1+2^2\right)+...+2^{57}\cdot\left(1+2^2\right)+2^2\cdot\left(1+2^2\right)+...+2^{58}\cdot\left(1+2^2\right)\\ =\left(1+2^2\right)\cdot\left(2+2^5+...+2^{57}+2^2+...+2^{59}\right)\\ =5\cdot\left(2+2^5+...+2^{57}+2^2+...+2^{59}\right)⋮5\)

Vậy \(D⋮5\)

\(D=2+2^2+2^3+...+2^{60}\\ =\left(2+2^2+2^3\right)+\left(2^4+2^5+2^6\right)+...+\left(2^{58}+2^{59}+2^{60}\right)\\ =2\cdot\left(1+2+2^2\right)+2^4\cdot\left(1+2+2^2\right)+...+2^{58}\cdot\left(1+2+2^2\right)\\ =\left(1+2+2^2\right)\cdot\left(2+2^4+...+2^{58}\right)\\ =7\cdot\left(2+2^4+...+2^{58}\right)⋮7\)

Ta có:

\(D⋮3;D⋮5\Rightarrow D⋮3\cdot5\Leftrightarrow D⋮15\)

\(D⋮3;D⋮7\Rightarrow D⋮3\cdot7\Leftrightarrow D⋮21\)

Vậy \(D⋮15;D⋮21\)

Mình chỉ làm mẫu 1 câu thui nha:

\(A=17^{18}-17^{16}\)

\(A=17^{16}.17^2-17^{16}.1\)

\(A=17^{16}\left(17^2-1\right)\)

\(A=17^{16}.288\)

\(A=17^{16}.16.18\)

\(A⋮18\left(đpcm\right)\)

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