Bài 7: Biến đổi đơn giản biểu thức chứa căn thức bậc hai (tiếp theo)
Hướng dẫn giải Bài 54 (Trang 30 SGK Toán 9, Tập 1)
<p><strong>B&agrave;i 54 (Trang 30 SGK To&aacute;n 9, Tập 1):</strong></p> <p>R&uacute;t gọn c&aacute;c biểu thức sau (giả thiết c&aacute;c biểu thức chữ đều c&oacute; nghĩa):</p> <p><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mrow><mn>2</mn><mo>+</mo><msqrt><mn>2</mn></msqrt></mrow><mrow><mn>1</mn><mo>+</mo><msqrt><mn>2</mn></msqrt></mrow></mfrac><mo>;</mo><mo>&#160;</mo><mo>&#160;</mo><mo>&#160;</mo><mo>&#160;</mo><mo>&#160;</mo><mo>&#160;</mo><mo>&#160;</mo><mfrac><mrow><msqrt><mn>15</mn></msqrt><mo>-</mo><msqrt><mn>5</mn></msqrt></mrow><mrow><mn>1</mn><mo>-</mo><msqrt><mn>3</mn></msqrt></mrow></mfrac><mo>;</mo><mo>&#160;</mo><mo>&#160;</mo><mo>&#160;</mo><mo>&#160;</mo><mo>&#160;</mo><mo>&#160;</mo><mfrac><mrow><mn>2</mn><msqrt><mn>3</mn></msqrt><mo>-</mo><msqrt><mn>6</mn></msqrt></mrow><mrow><msqrt><mn>8</mn></msqrt><mo>-</mo><mn>2</mn></mrow></mfrac><mo>;</mo><mo>&#160;</mo><mo>&#160;</mo><mo>&#160;</mo><mo>&#160;</mo><mo>&#160;</mo><mo>&#160;</mo><mfrac><mrow><mi mathvariant="normal">a</mi><mo>-</mo><msqrt><mi mathvariant="normal">a</mi></msqrt></mrow><mrow><mn>1</mn><mo>-</mo><msqrt><mi mathvariant="normal">a</mi></msqrt></mrow></mfrac><mo>;</mo><mo>&#160;</mo><mo>&#160;</mo><mo>&#160;</mo><mo>&#160;</mo><mo>&#160;</mo><mo>&#160;</mo><mo>&#160;</mo><mfrac><mrow><mi mathvariant="normal">p</mi><mo>-</mo><mn>2</mn><msqrt><mi mathvariant="normal">p</mi></msqrt></mrow><mrow><msqrt><mi mathvariant="normal">p</mi></msqrt><mo>-</mo><mn>2</mn></mrow></mfrac><mo>.</mo></math></p> <p>&nbsp;</p> <p><strong><span style="text-decoration: underline;"><em>Hướng dẫn giải:</em></span></strong></p> <p><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mrow><mn>2</mn><mo>+</mo><msqrt><mn>2</mn></msqrt></mrow><mrow><mn>1</mn><mo>+</mo><msqrt><mn>2</mn></msqrt></mrow></mfrac><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mfrac><mrow><msup><mrow><mo>(</mo><msqrt><mn>2</mn></msqrt><mo>)</mo></mrow><mn>2</mn></msup><mo>+</mo><msqrt><mn>2</mn></msqrt></mrow><mrow><mn>1</mn><mo>+</mo><msqrt><mn>2</mn></msqrt></mrow></mfrac><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mfrac><mrow><msqrt><mn>2</mn></msqrt><mo>(</mo><msqrt><mn>2</mn></msqrt><mo>+</mo><mn>1</mn><mo>)</mo></mrow><mrow><mn>1</mn><mo>+</mo><msqrt><mn>2</mn></msqrt></mrow></mfrac><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><msqrt><mn>2</mn></msqrt><mo>;</mo></math></p> <p>C&aacute;ch kh&aacute;c:<em><strong> </strong></em><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mrow><mn>2</mn><mo>+</mo><msqrt><mn>2</mn></msqrt></mrow><mrow><mn>1</mn><mo>+</mo><msqrt><mn>2</mn></msqrt></mrow></mfrac><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mfrac><mrow><mo>(</mo><mn>2</mn><mo>+</mo><msqrt><mn>2</mn></msqrt><mo>)</mo><mo>(</mo><mn>1</mn><mo>-</mo><msqrt><mn>2</mn></msqrt><mo>)</mo></mrow><mrow><mo>(</mo><mn>1</mn><mo>+</mo><msqrt><mn>2</mn></msqrt><mo>)</mo><mo>(</mo><mn>1</mn><mo>-</mo><msqrt><mn>2</mn></msqrt><mo>)</mo></mrow></mfrac><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mfrac><mrow><mn>2</mn><mo>-</mo><mn>2</mn><msqrt><mn>2</mn></msqrt><mo>+</mo><msqrt><mn>2</mn></msqrt><mo>-</mo><msup><mrow><mo>(</mo><msqrt><mn>2</mn></msqrt><mo>)</mo></mrow><mn>2</mn></msup></mrow><mrow><mn>1</mn><mo>-</mo><msup><mrow><mo>(</mo><msqrt><mn>2</mn></msqrt><mo>)</mo></mrow><mn>2</mn></msup></mrow></mfrac><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mfrac><mrow><mn>2</mn><mo>-</mo><msqrt><mn>2</mn></msqrt><mo>-</mo><mn>2</mn></mrow><mrow><mn>1</mn><mo>-</mo><mn>2</mn></mrow></mfrac><mo>=</mo><mfrac><mrow><mo>-</mo><msqrt><mn>2</mn></msqrt></mrow><mrow><mo>-</mo><mn>1</mn></mrow></mfrac><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><msqrt><mn>2</mn></msqrt><mo>.</mo></math><span class="mce-nbsp-wrap" contenteditable="false">&nbsp;&nbsp;&nbsp;</span><span class="mce-nbsp-wrap" contenteditable="false">&nbsp;&nbsp;&nbsp;</span><span class="mce-nbsp-wrap" contenteditable="false">&nbsp;&nbsp;&nbsp;</span><span class="mce-nbsp-wrap" contenteditable="false">&nbsp;&nbsp;&nbsp;</span><span class="mce-nbsp-wrap" contenteditable="false">&nbsp;&nbsp;&nbsp;</span>&nbsp;</p> <p><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mrow><msqrt><mn>15</mn></msqrt><mo>-</mo><msqrt><mn>5</mn></msqrt></mrow><mrow><mn>1</mn><mo>-</mo><msqrt><mn>3</mn></msqrt></mrow></mfrac><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mfrac><mrow><msqrt><mn>3</mn><mo>.</mo><mn>5</mn></msqrt><mo>-</mo><msqrt><mn>5</mn></msqrt></mrow><mrow><mn>1</mn><mo>-</mo><msqrt><mn>3</mn></msqrt></mrow></mfrac><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mfrac><mrow><msqrt><mn>5</mn></msqrt><mo>(</mo><msqrt><mn>3</mn></msqrt><mo>-</mo><mn>1</mn><mo>)</mo></mrow><mrow><mn>1</mn><mo>-</mo><msqrt><mn>3</mn></msqrt></mrow></mfrac><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mo>-</mo><msqrt><mn>5</mn></msqrt><mo>;</mo></math></p> <p><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mrow><mn>2</mn><msqrt><mn>3</mn></msqrt><mo>-</mo><msqrt><mn>6</mn></msqrt></mrow><mrow><msqrt><mn>8</mn></msqrt><mo>-</mo><mn>2</mn></mrow></mfrac><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mfrac><mrow><msqrt><msup><mn>2</mn><mn>2</mn></msup><mo>.</mo><mn>3</mn></msqrt><mo>-</mo><msqrt><mn>6</mn></msqrt></mrow><mrow><msqrt><mn>4</mn><mo>.</mo><mn>2</mn></msqrt><mo>-</mo><mn>2</mn></mrow></mfrac><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mfrac><mrow><msqrt><mn>2</mn></msqrt><mo>.</mo><mn>6</mn><mo>-</mo><msqrt><mn>6</mn></msqrt></mrow><mrow><mn>2</mn><msqrt><mn>2</mn></msqrt><mo>-</mo><mn>2</mn></mrow></mfrac><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mfrac><mrow><msqrt><mn>6</mn></msqrt><mo>(</mo><msqrt><mn>2</mn></msqrt><mo>-</mo><mn>1</mn><mo>)</mo></mrow><mrow><mn>2</mn><mo>(</mo><msqrt><mn>2</mn></msqrt><mo>-</mo><mn>2</mn><mo>)</mo></mrow></mfrac><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mfrac><msqrt><mn>6</mn></msqrt><mn>2</mn></mfrac><mo>;</mo></math></p> <p><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mrow><mi mathvariant="normal">a</mi><mo>-</mo><msqrt><mi mathvariant="normal">a</mi></msqrt></mrow><mrow><mn>1</mn><mo>-</mo><msqrt><mi mathvariant="normal">a</mi></msqrt></mrow></mfrac><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mfrac><mrow><msup><mrow><mo>(</mo><msqrt><mi mathvariant="normal">a</mi></msqrt><mo>)</mo></mrow><mn>2</mn></msup><mo>-</mo><msqrt><mi mathvariant="normal">a</mi></msqrt></mrow><mrow><mn>1</mn><mo>-</mo><msqrt><mi mathvariant="normal">a</mi></msqrt></mrow></mfrac><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mfrac><mrow><msqrt><mi mathvariant="normal">a</mi></msqrt><mo>(</mo><msqrt><mi mathvariant="normal">a</mi></msqrt><mo>-</mo><mn>1</mn><mo>)</mo></mrow><mrow><mn>1</mn><mo>-</mo><msqrt><mi mathvariant="normal">a</mi></msqrt></mrow></mfrac><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mo>-</mo><msqrt><mi mathvariant="normal">a</mi></msqrt><mo>;</mo></math></p> <p><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mrow><mi mathvariant="normal">p</mi><mo>-</mo><mn>2</mn><msqrt><mi mathvariant="normal">p</mi></msqrt></mrow><mrow><msqrt><mi mathvariant="normal">p</mi></msqrt><mo>-</mo><mn>2</mn></mrow></mfrac><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mfrac><mrow><msup><mrow><mo>(</mo><msqrt><mi mathvariant="normal">p</mi></msqrt><mo>)</mo></mrow><mn>2</mn></msup><mo>-</mo><mn>2</mn><msqrt><mi mathvariant="normal">p</mi></msqrt></mrow><mrow><msqrt><mi mathvariant="normal">p</mi></msqrt><mo>-</mo><mn>2</mn></mrow></mfrac><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mfrac><mrow><msqrt><mi mathvariant="normal">p</mi></msqrt><mo>(</mo><msqrt><mi mathvariant="normal">p</mi></msqrt><mo>-</mo><mn>2</mn><mo>)</mo></mrow><mrow><msqrt><mi mathvariant="normal">p</mi></msqrt><mo>-</mo><mn>2</mn></mrow></mfrac><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><msqrt><mi mathvariant="normal">p</mi></msqrt><mo>.</mo></math> <span class="mce-nbsp-wrap" contenteditable="false">&nbsp;&nbsp;&nbsp;</span><span class="mce-nbsp-wrap" contenteditable="false">&nbsp;&nbsp;&nbsp;</span><span class="mce-nbsp-wrap" contenteditable="false">&nbsp;&nbsp;&nbsp;</span><span class="mce-nbsp-wrap" contenteditable="false">&nbsp;&nbsp;&nbsp;</span><span class="mce-nbsp-wrap" contenteditable="false">&nbsp;&nbsp;&nbsp;</span><span class="mce-nbsp-wrap" contenteditable="false">&nbsp;&nbsp;&nbsp;</span><span class="mce-nbsp-wrap" contenteditable="false">&nbsp;&nbsp;&nbsp;</span><span class="mce-nbsp-wrap" contenteditable="false">&nbsp;&nbsp;&nbsp;</span><span class="mce-nbsp-wrap" contenteditable="false">&nbsp;&nbsp;&nbsp;</span><span class="mce-nbsp-wrap" contenteditable="false">&nbsp;&nbsp;&nbsp;</span></p>
Hướng dẫn Giải Bài 54 (trang 30, SGK Toán 9, Tập 1)
GV: GV colearn
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Hướng dẫn Giải Bài 54 (trang 30, SGK Toán 9, Tập 1)
GV: GV colearn