Bài 6 trang 93 Tài liệu dạy – học toán 6 tập 1, Tìm số tự nhiên x, biết...

Tìm số tự nhiên x, biết :

$\eqalign{  & a)\;\left( {x + 83} \right) - 37 = 56  \cr   & b)\;128 - 3\left( {x - 5} \right) = 17  \cr   & c)\;20 + 3x = {5^6}:{5^3}  \cr   & d)\;\left[ {\left( {2x + 1} \right).3 + 55} \right]:4 = 25  \cr   & e)\;\left( {4x - {4^2}} \right){.7^3} = {4.7^4}  \cr   & g)\;{6^2}{.2^2}.5:\left[ {3.12 - \left( {2x - 6} \right)} \right] = {2^3}.5  \cr   & h)\;8x - 3x = {6^{27}}:{6^{25}} + 44:11  \cr   & i)\;3 \;\vdots \left( {x + 1} \right). \cr}$

$\eqalign{  & a)\left( {x + 83} \right) - 37 = 56  \cr   & x + 83 = 56 + 37  \cr   & x + 83 = 93  \cr   & x = 93 - 83  \cr   & x = 10  \cr   & b)128 - 3\left( {x - 5} \right) = 17  \cr   & 3(x - 5) = 128 - 17  \cr   & 3(x - 5) = 111  \cr   & x - 5 = 111:3  \cr   & x - 5 = 37  \cr   & x = 37 + 5  \cr   & x = 42  \cr   & c)20 + 3x = {5^6}:{5^3}  \cr   & 20 + 3x = {5^{6 - 3}}  \cr   & 20 + 3x = {5^3}  \cr   & 20 + 3x = 125  \cr   & 3x = 125 - 20  \cr   & 3x = 105  \cr   & x = 105:3  \cr   & x = 35  \cr   &  \cr}$

$\eqalign{  & d)\left[ {\left( {2x + 1} \right).3 + 55} \right]:4 = 25  \cr   & (2x + 1).3 + 55 = 25.4  \cr   & (2x + 1).3 + 55 = 100  \cr   & (2x + 1).3 = 100 - 55  \cr   & (2x + 1).3 = 45  \cr   & 2x + 1 = 45:3  \cr   & 2x + 1 = 15  \cr   & 2x = 15 - 1  \cr   & 2x = 14  \cr   & x = 14:2  \cr   & x = 7  \cr   & e)\left( {4x - {4^2}} \right){.7^3} = {4.7^4}  \cr   & 4x - 16 = ({4.7^4}):{7^3}  \cr   & 4x - 16 = 4.7  \cr   & 4x - 16 = 28  \cr   & 4x = 28 + 16  \cr   & 4x = 44  \cr   & x = 44:4  \cr   & x = 11 \cr}$

$\eqalign{  &   \cr   & g){6^2}{.2^2}.5:\left[ {3.12 - \left( {2x - 6} \right)} \right] = {2^3}.5  \cr   & 3.12 - (2x - 6) = ({6^2}{.2^2}.5):({2^3}.5)  \cr   & 36 - (2x - 6) = {6^2}:2  \cr   & 36 - (2x - 6) = 36:2  \cr   & 36 - (2x - 6) = 18  \cr   & 2x - 6 = 36 - 18  \cr   & 2x - 6 = 18  \cr   & 2x = 18 + 6  \cr   & 2x = 24  \cr   & x = 24:2 \Leftrightarrow x = 12  \cr   & h)8x - 3x = {6^{27}}:{6^{25}} + 44:11  \cr   & (8 - 3)x = {6^{27 - 25}} + 4  \cr   & 5x = {6^2} + 4  \cr   & 5x = 36 + 4  \cr   & 5x = 40  \cr   & x = 40:5 \Leftrightarrow x = 8  \cr   & i)\;3 \;\vdots \left( {x + 1} \right)  \cr   &  \Rightarrow (x + 1) \in U(3) = {\rm{\{ }}1;3\}   \cr   &  \Rightarrow x \in {\rm{\{ 0;2\} }} \cr}$