Bài 3: Liên hệ giữa phép nhân và phép khai phương
Hướng dẫn giải Bài 17 (Trang 14 SGK Toán 9, Tập 1)
<p><strong>B&agrave;i 17 (Trang 14 SGK To&aacute;n 9, Tập 1):</strong></p> <p>&Aacute;p dụng quy tắc khai phương một t&iacute;ch, h&atilde;y t&iacute;nh&nbsp;</p> <p><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>a</mi><mo>)</mo><mo>&#160;</mo><msqrt><mn>0</mn><mo>,</mo><mn>09</mn><mo>.</mo><mn>64</mn><mo>&#160;</mo></msqrt><mo>;</mo><mspace linebreak="newline"/><mspace linebreak="newline"/><mi>b</mi><mo>)</mo><mo>&#160;</mo><msqrt><msup><mn>2</mn><mn>4</mn></msup><mo>.</mo><msup><mfenced><mrow><mo>-</mo><mn>7</mn></mrow></mfenced><mn>2</mn></msup></msqrt><mo>;</mo><mspace linebreak="newline"/><mspace linebreak="newline"/><mi>c</mi><mo>)</mo><mo>&#160;</mo><msqrt><mn>12</mn><mo>,</mo><mn>1</mn><mo>.</mo><mn>360</mn></msqrt><mo>;</mo><mspace linebreak="newline"/><mspace linebreak="newline"/><mi>d</mi><mo>)</mo><mo>&#160;</mo><msqrt><msup><mn>2</mn><mn>2</mn></msup><mo>.</mo><msup><mn>3</mn><mn>4</mn></msup></msqrt></math></p> <p>&nbsp;</p> <p><strong><span style="text-decoration: underline;"><em>Hướng dẫn giải:</em></span></strong></p> <p>a)&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msqrt><mn>0</mn><mo>,</mo><mn>09</mn><mo>.</mo><mn>64</mn></msqrt><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><msqrt><mn>0</mn><mo>,</mo><mn>09</mn></msqrt><mo>&#160;</mo><mo>.</mo><mo>&#160;</mo><msqrt><mn>64</mn></msqrt><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>0</mn><mo>,</mo><mn>3</mn><mo>&#160;</mo><mo>.</mo><mo>&#160;</mo><mn>8</mn><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>2</mn><mo>,</mo><mn>4</mn><mo>.</mo></math></p> <p>b)&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msqrt><msup><mn>2</mn><mn>4</mn></msup><mo>.</mo><msup><mfenced><mrow><mo>-</mo><mn>7</mn></mrow></mfenced><mn>2</mn></msup></msqrt><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><msqrt><msup><mn>2</mn><mn>4</mn></msup></msqrt><mo>&#160;</mo><mo>.</mo><mo>&#160;</mo><msqrt><msup><mfenced><mrow><mo>-</mo><mn>7</mn></mrow></mfenced><mn>2</mn></msup></msqrt><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mfenced open="|" close="|"><msup><mn>2</mn><mn>2</mn></msup></mfenced><mo>.</mo><mfenced open="|" close="|"><mrow><mo>-</mo><mn>7</mn></mrow></mfenced><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>4</mn><mo>.</mo><mn>7</mn><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>28</mn></math></p> <p>c)&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msqrt><mn>12</mn><mo>,</mo><mn>1</mn><mo>.</mo><mn>360</mn></msqrt><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><msqrt><mn>121</mn><mo>.</mo><mn>36</mn></msqrt><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><msqrt><mn>121</mn></msqrt><mo>.</mo><msqrt><mn>36</mn></msqrt><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>11</mn><mo>.</mo><mn>6</mn><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>66</mn></math></p> <p>d)&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msqrt><msup><mn>2</mn><mn>2</mn></msup><mo>.</mo><msup><mn>3</mn><mn>4</mn></msup></msqrt><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><msqrt><msup><mn>2</mn><mn>2</mn></msup><mo>.</mo><msup><mfenced><msup><mn>3</mn><mn>2</mn></msup></mfenced><mn>2</mn></msup></msqrt><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><msqrt><msup><mn>2</mn><mn>2</mn></msup></msqrt><mo>&#160;</mo><mo>.</mo><msqrt><msup><mn>9</mn><mn>2</mn></msup></msqrt><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>2</mn><mo>.</mo><mn>9</mn><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>18</mn><mo>.</mo></math></p>
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