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1.=(x-2)(x 2+2x+7)+2(x-2)(x+2)-5(x-2) = 0
=>(x-2)(x 2+2x+7+2x+4-5) = 0
=>(x-2)(x 2+4x+6) = 0
Mà x 2+4x+6 (E Z)
=> x 2+4x+6 > 0
Vậy (x-2)=0 => x = 2
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 1 : Tìm x, biết :
\(\left(x-2\right)\left(x^2+2x+7\right)+2\left(x^2-4\right)-5\left(x-2\right)=0\)
\(\Rightarrow\left(x-2\right)\left(x^2+2x+7\right)+2\left(x-2\right)\left(x+2\right)-5\left(x-2\right)=0\) \(\Rightarrow\left(x-2\right)\left(x^2+2x+7\right)+\left(x-2\right)\left(2\left(x+2\right)-5\right)=0\)
\(\Rightarrow\left(x-2\right)\left(x^2+2x+7+2\left(x+2\right)-5\right)=0\)
\(\Rightarrow\left(x-2\right)\left(x^2+2x+7+2x+4-5\right)=0\)
\(\Rightarrow\left(x-2\right)\left(x^2+4x+6\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x-2=0\\x^2+4x+6=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=2\\\left(x+2\right)^2+2>0\end{matrix}\right.\Rightarrow x=2\)
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a: \(=\left(2^3-1\right)\left(2^6+2^3+1\right)=73\cdot7⋮73\)
b: Đề sai rồi bạn
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\(a;43^2+43.17=43\left(43+17\right)=43.60⋮60\left(đpcm\right)\)
\(b;27^5-3^{11}=3^{15}-3^{11}=3^{11}\left(3^4-1\right)=3^{11}.80⋮80\left(đpcm\right)\)
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a/ 29 - 1 = \(\left(2^3\right)^3\) - 1 = 83 - 1 = (8-1)( 82 +8.1 + 1) = (8-1).73 \(⋮\) 73
b/ 56 - 104 = 54(52 - 24) = 54 (25 - 16) = 54 .9 chia hết cho 9
c, (n+6)2-(n-6)2=(n+6-n+6)(n+6+n-6)(hđt số 3
=12 .2n=24n
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có 2^9 - 1 = 8^3-1 = (8-1)(8^2+8+1)
= 7*73
vì 73 chia hết cho 73 =>7*73 chia hết cho 73
Hay 2^9-1 chia hết cho 73
cảm ơn