Question

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1,tìm x

[ ( 6 . x - 72 ) : 2 - 84 ] .28 = 5628

dấu . kia là nhân nhé

2, chứng minh A chia hết cho 3 

A= 2 + 2² + 2^{3 +} 2⁴ + 2⁵ + 2⁶ + 2⁷ + 2⁸ + 2⁹ +2¹⁰

^{nhanh lên nhé các bạn ưi}

Answer 1

\(\left[\left(6x-72\right):2-84\right].28=5628\)

\(\Rightarrow\left[\left(6x-72\right):2-84\right]=201\)

\(\Rightarrow\left[\left(6x-72\right):2\right]=285\)

\(\Rightarrow6x-72=570\)

\(\Rightarrow6x=642\)

\(\Rightarrow x=107\)

 

Answer 2

\(A=2+2^2+2^3+2^4+...+2^{10}\)

\(A=\left(2+2^2\right)\left(2^3+2^4\right)+...+\left(2^9+2^{10}\right)\)

\(A=3.2+3.2^3+3.2^5+...+3.2^9\)

\(A=3\left(2+2^3+2^5+...+2^9\right)⋮3\)

Vậy A chia hết cho 3