Chọn câu sai. A. 5x + 5/5x = x + 1/x B. x^2 - 4/x + 2 = x - 2 C. x + 3/x^2 - 9 = 1/x - 3 D. 5x + 5/5x = 5
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13/09/2024
Chọn câu sai.
A. \[\frac{{{\rm{5x + 5}}}}{{{\rm{5x}}}}{\rm{ = }}\frac{{{\rm{x + 1}}}}{{\rm{x}}}\]
B. \[\frac{{{{\rm{x}}^{\rm{2}}} - {\rm{4}}}}{{{\rm{x + 2}}}}{\rm{ = x}} - {\rm{2}}\]
C. \[\frac{{{\rm{x + 3}}}}{{{{\rm{x}}^{\rm{2}}} - {\rm{9}}}}{\rm{ = }}\frac{{\rm{1}}}{{{\rm{x}} - {\rm{3}}}}\]
D. \[\frac{{{\rm{5x + 5}}}}{{{\rm{5x}}}}{\rm{ = 5}}\]
Trả lời
Lời giải
Đáp án đúng là: D
• \[\left( {5x + 5} \right)x = 5\left( {x + 1} \right)x = 5x\left( {x + 1} \right) \Rightarrow \frac{{5x + 5}}{{5x}} = \frac{{x + 1}}{x}\]
• \[\left( {x - 2} \right)\left( {x + 2} \right) = {x^2} - 2x + 2x - 4 = {x^2} - 4 \Rightarrow \frac{{{x^2} - 4}}{{x + 2}} = x - 2\]
• \[\left( {x + 3} \right)\left( {x - 3} \right) = {x^2} + 3x - 3x - 9 = {x^2} - 9 \Rightarrow \frac{{x + 3}}{{{x^2} - 9}} = \frac{1}{{x - 3}}\]
• \[5\,.\,5x = 25x \ne 5x + 5 \Rightarrow \frac{{5x + 5}}{{5x}} \ne 5\]
