Bài 5: Diện tích xung quanh của hình lăng trụ đứng
Hướng dẫn giải Bài 24 (Trang 111 SGK Toán Hình học 8, Tập 2)
<p>Quan sát lăng trụ đứng tam giác (h.103) rồi điền số thích hợp vào các ô trống ở bảng sau:</p>
<p><img class="wscnph" src="https://static.colearn.vn:8413/v1.0/upload/library/01032022/ee738ee0-42c9-45db-a91e-118fc9c2907c.PNG" /></p>
<table style="border-collapse: collapse; width: 100%; height: 161.344px;" border="1">
<tbody>
<tr style="height: 22.3906px;">
<td style="width: 26.6529%; height: 22.3906px;">a (cm)</td>
<td style="width: 18.7978%; height: 22.3906px;">5</td>
<td style="width: 18.8055%; height: 22.3906px;">3</td>
<td style="width: 17.1488%; height: 22.3906px;">12</td>
<td style="width: 18.595%; height: 22.3906px;">7</td>
</tr>
<tr style="height: 22.3906px;">
<td style="width: 26.6529%; height: 22.3906px;">b (cm)</td>
<td style="width: 18.7978%; height: 22.3906px;">6</td>
<td style="width: 18.8055%; height: 22.3906px;">2</td>
<td style="width: 17.1488%; height: 22.3906px;">15</td>
<td style="width: 18.595%; height: 22.3906px;"> </td>
</tr>
<tr style="height: 22.3906px;">
<td style="width: 26.6529%; height: 22.3906px;">c (cm)</td>
<td style="width: 18.7978%; height: 22.3906px;">7</td>
<td style="width: 18.8055%; height: 22.3906px;"> </td>
<td style="width: 17.1488%; height: 22.3906px;">13</td>
<td style="width: 18.595%; height: 22.3906px;">6</td>
</tr>
<tr style="height: 22.3906px;">
<td style="width: 26.6529%; height: 22.3906px;">h (cm)</td>
<td style="width: 18.7978%; height: 22.3906px;">10</td>
<td style="width: 18.8055%; height: 22.3906px;">5</td>
<td style="width: 17.1488%; height: 22.3906px;"> </td>
<td style="width: 18.595%; height: 22.3906px;"> </td>
</tr>
<tr style="height: 44.7813px;">
<td style="width: 26.6529%; height: 44.7813px;">Chu vi đáy (cm) </td>
<td style="width: 18.7978%; height: 44.7813px;"> </td>
<td style="width: 18.8055%; height: 44.7813px;">9</td>
<td style="width: 17.1488%; height: 44.7813px;"> </td>
<td style="width: 18.595%; height: 44.7813px;">21</td>
</tr>
<tr style="height: 27px;">
<td style="width: 26.6529%; height: 27px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>S</mi><mrow><mi>x</mi><mi>q</mi></mrow></msub><mfenced><mrow><mi>c</mi><msup><mi>m</mi><mn>2</mn></msup></mrow></mfenced></math></td>
<td style="width: 18.7978%; height: 27px;"> </td>
<td style="width: 18.8055%; height: 27px;"> </td>
<td style="width: 17.1488%; height: 27px;">80</td>
<td style="width: 18.595%; height: 27px;">63</td>
</tr>
</tbody>
</table>
<p><strong>Giải:</strong></p>
<p>Các số phải điền vào các ô trống được tính như sau:</p>
<p>+ Ở cột 1: Chu vi đáy: <math xmlns="http://www.w3.org/1998/Math/MathML"><mn>5</mn><mo>+</mo><mn>6</mn><mo>+</mo><mn>7</mn><mo> </mo><mo>=</mo><mo> </mo><mn>18</mn><mfenced><mrow><mi>c</mi><mi>m</mi></mrow></mfenced></math>; <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>S</mi><mrow><mi>x</mi><mi>q</mi></mrow></msub><mo>=</mo><mn>18</mn><mi>x</mi><mn>10</mn><mo>=</mo><mn>180</mn><mfenced><mrow><mi>c</mi><msup><mi>m</mi><mn>2</mn></msup></mrow></mfenced></math></p>
<p>+ Ở cột 2: c = <math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced><mrow><mn>9</mn><mo>-</mo><mn>3</mn><mo>-</mo><mn>2</mn></mrow></mfenced><mo>=</mo><mn>4</mn><mfenced><mrow><mi>c</mi><mi>m</mi></mrow></mfenced><mo>;</mo><mo> </mo><msub><mi>S</mi><mrow><mi>x</mi><mi>q</mi></mrow></msub><mo>=</mo><mn>9</mn><mi>x</mi><mn>5</mn><mo>=</mo><mn>45</mn><mfenced><mrow><mi>c</mi><msup><mi>m</mi><mn>2</mn></msup></mrow></mfenced></math></p>
<p>+ Ở cột 3: Chu vi đáy: <math xmlns="http://www.w3.org/1998/Math/MathML"><mn>12</mn><mo>+</mo><mn>15</mn><mo>+</mo><mn>13</mn><mo>=</mo><mn>40</mn><mfenced><mrow><mi>c</mi><mi>m</mi></mrow></mfenced><mo>;</mo><mo> </mo><mi>h</mi><mo>=</mo><mn>80</mn><mo> </mo><mo>:</mo><mo> </mo><mn>40</mn><mo>=</mo><mn>2</mn><mfenced><mrow><mi>c</mi><mi>m</mi></mrow></mfenced></math></p>
<p>+ Ở cột 4: <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>b</mi><mo>=</mo><mn>21</mn><mo>-</mo><mfenced><mrow><mn>7</mn><mo>+</mo><mn>6</mn></mrow></mfenced><mo>=</mo><mn>8</mn><mfenced><mrow><mi>c</mi><mi>m</mi></mrow></mfenced><mo>;</mo><mo> </mo><mi>h</mi><mo>=</mo><mn>63</mn><mo>:</mo><mn>21</mn><mo>=</mo><mn>3</mn><mfenced><mrow><mi>c</mi><mi>m</mi></mrow></mfenced></math></p>
<p>Kết quả ta có bảng sau:</p>
<table style="border-collapse: collapse; width: 100%; height: 161.344px;" border="1">
<tbody>
<tr style="height: 22.3906px;">
<td style="width: 26.6529%; height: 22.3906px;">a (cm)</td>
<td style="width: 18.7978%; height: 22.3906px;">5</td>
<td style="width: 18.8055%; height: 22.3906px;">3</td>
<td style="width: 17.1488%; height: 22.3906px;">12</td>
<td style="width: 18.595%; height: 22.3906px;">7</td>
</tr>
<tr style="height: 22.3906px;">
<td style="width: 26.6529%; height: 22.3906px;">b (cm)</td>
<td style="width: 18.7978%; height: 22.3906px;">6</td>
<td style="width: 18.8055%; height: 22.3906px;">2</td>
<td style="width: 17.1488%; height: 22.3906px;">15</td>
<td style="width: 18.595%; height: 22.3906px;"><strong>8</strong></td>
</tr>
<tr style="height: 22.3906px;">
<td style="width: 26.6529%; height: 22.3906px;">c (cm)</td>
<td style="width: 18.7978%; height: 22.3906px;">7</td>
<td style="width: 18.8055%; height: 22.3906px;"><strong>4</strong></td>
<td style="width: 17.1488%; height: 22.3906px;">13</td>
<td style="width: 18.595%; height: 22.3906px;">6</td>
</tr>
<tr style="height: 22.3906px;">
<td style="width: 26.6529%; height: 22.3906px;">h (cm)</td>
<td style="width: 18.7978%; height: 22.3906px;">10</td>
<td style="width: 18.8055%; height: 22.3906px;">5</td>
<td style="width: 17.1488%; height: 22.3906px;"><strong>2</strong></td>
<td style="width: 18.595%; height: 22.3906px;"><strong>3</strong></td>
</tr>
<tr style="height: 44.7813px;">
<td style="width: 26.6529%; height: 44.7813px;">Chu vi đáy (cm) </td>
<td style="width: 18.7978%; height: 44.7813px;"><strong>18</strong></td>
<td style="width: 18.8055%; height: 44.7813px;">9</td>
<td style="width: 17.1488%; height: 44.7813px;"><strong>40</strong></td>
<td style="width: 18.595%; height: 44.7813px;">21</td>
</tr>
<tr style="height: 27px;">
<td style="width: 26.6529%; height: 27px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>S</mi><mrow><mi>x</mi><mi>q</mi></mrow></msub><mfenced><mrow><mi>c</mi><msup><mi>m</mi><mn>2</mn></msup></mrow></mfenced></math></td>
<td style="width: 18.7978%; height: 27px;"><strong>180</strong></td>
<td style="width: 18.8055%; height: 27px;"><strong>45</strong></td>
<td style="width: 17.1488%; height: 27px;">80</td>
<td style="width: 18.595%; height: 27px;">63</td>
</tr>
</tbody>
</table>
<p> </p>
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