Bài 4: Hình lăng trụ đứng
Hướng dẫn giải Bài 21 (Trang 108 SGK Toán Hình học 8, Tập 2)
<p><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>A</mi><mi>B</mi><mi>C</mi><mo>.</mo><mi>A</mi><mo>'</mo><mi>B</mi><mo>'</mo><mi>C</mi><mo>'</mo></math><span style="vertical-align: inherit;"><span style="vertical-align: inherit;">is a lăng trụ đứng tam giác (h.98).</span></span></p>
<p><img class="wscnph" style="max-width: 100%;" src="https://static.colearn.vn:8413/v1.0/upload/library/03052022/b1a6eca2-40c6-4e55-9bc9-7a53b8fd9adf.PNG" /></p>
<p><span style="vertical-align: inherit;"><span style="vertical-align: inherit;">a) Những bài hát cặp đôi nào với nhau?</span></span></p>
<p><span style="vertical-align: inherit;"><span style="vertical-align: inherit;">b) Những cặp mặt vuông góc nào với nhau?</span></span></p>
<p><span style="vertical-align: inherit;"><span style="vertical-align: inherit;">c) Sử dụng ký hiệu "//" và "⊥" để điền vào các ô trống ở bảng sau:</span></span></p>
<table style="border-collapse: collapse; width: 102.16%; height: 126.141px;" border="1">
<tbody>
<tr style="height: 50.1875px;">
<td style="width: 19.0678%; height: 50.1875px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac bevelled="true"><mrow><mi>C</mi><mi>ạ</mi><mi>n</mi><mi>h</mi></mrow><mrow><mi>M</mi><mi>ặ</mi><mi>t</mi></mrow></mfrac></math></td>
<td style="width: 9.95763%; height: 50.1875px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>A</mi><mi>A</mi><mo>'</mo></math></td>
<td style="width: 10.3814%; height: 50.1875px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>C</mi><mi>C</mi><mo>'</mo></math></td>
<td style="width: 9.74576%; height: 50.1875px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>B</mi><mi>B</mi><mo>'</mo></math></td>
<td style="width: 9.11017%; height: 50.1875px;"><span style="vertical-align: inherit;"><span style="vertical-align: inherit;">AC'</span></span></td>
<td style="width: 8.89831%; height: 50.1875px;"><span style="vertical-align: inherit;"><span style="vertical-align: inherit;">B'C '</span></span></td>
<td style="width: 9.11017%; height: 50.1875px;"><span style="vertical-align: inherit;"><span style="vertical-align: inherit;">A'B '</span></span></td>
<td style="width: 7.83898%; height: 50.1875px;"><span style="vertical-align: inherit;"><span style="vertical-align: inherit;">AC</span></span></td>
<td style="width: 7.83898%; height: 50.1875px;"><span style="vertical-align: inherit;"><span style="vertical-align: inherit;">CB</span></span></td>
<td style="width: 8.05085%; height: 50.1875px;"><span style="vertical-align: inherit;"><span style="vertical-align: inherit;">AB</span></span></td>
</tr>
<tr style="height: 25.0938px;">
<td style="width: 19.0678%; height: 25.0938px;"><span style="vertical-align: inherit;"><span style="vertical-align: inherit;">ACB</span></span></td>
<td style="width: 9.95763%; height: 25.0938px;"> </td>
<td style="width: 10.3814%; height: 25.0938px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mo>⊥</mo></math></td>
<td style="width: 9.74576%; height: 25.0938px;"> </td>
<td style="width: 9.11017%; height: 25.0938px;"> </td>
<td style="width: 8.89831%; height: 25.0938px;"> </td>
<td style="width: 9.11017%; height: 25.0938px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mo>/</mo><mo>/</mo></math></td>
<td style="width: 7.83898%; height: 25.0938px;"> </td>
<td style="width: 7.83898%; height: 25.0938px;"> </td>
<td style="width: 8.05085%; height: 25.0938px;"> </td>
</tr>
<tr style="height: 25.7656px;">
<td style="width: 19.0678%; height: 25.7656px;"><span style="vertical-align: inherit;"><span style="vertical-align: inherit;"><span style="vertical-align: inherit;"><span style="vertical-align: inherit;">A'C'B'</span></span></span></span></td>
<td style="width: 9.95763%; height: 25.7656px;"> </td>
<td style="width: 10.3814%; height: 25.7656px;"> </td>
<td style="width: 9.74576%; height: 25.7656px;"> </td>
<td style="width: 9.11017%; height: 25.7656px;"> </td>
<td style="width: 8.89831%; height: 25.7656px;"> </td>
<td style="width: 9.11017%; height: 25.7656px;"> </td>
<td style="width: 7.83898%; height: 25.7656px;"> </td>
<td style="width: 7.83898%; height: 25.7656px;"> </td>
<td style="width: 8.05085%; height: 25.7656px;"> </td>
</tr>
<tr style="height: 25.0938px;">
<td style="width: 19.0678%; height: 25.0938px;"><span style="vertical-align: inherit;"><span style="vertical-align: inherit;">ABB'A'</span></span></td>
<td style="width: 9.95763%; height: 25.0938px;"> </td>
<td style="width: 10.3814%; height: 25.0938px;"> </td>
<td style="width: 9.74576%; height: 25.0938px;"> </td>
<td style="width: 9.11017%; height: 25.0938px;"> </td>
<td style="width: 8.89831%; height: 25.0938px;"> </td>
<td style="width: 9.11017%; height: 25.0938px;"> </td>
<td style="width: 7.83898%; height: 25.0938px;"> </td>
<td style="width: 7.83898%; height: 25.0938px;"> </td>
<td style="width: 8.05085%; height: 25.0938px;"> </td>
</tr>
</tbody>
</table>
<p><strong>Giải:</strong></p>
<p><strong>a)</strong> Những cặp mặt phẳng song song nhau: <math xmlns="http://www.w3.org/1998/Math/MathML"><mo>(</mo><mi>A</mi><mi>B</mi><mi>C</mi><mo>)</mo><mo> </mo><mo>/</mo><mo>/</mo><mo> </mo><mo>(</mo><mi>A</mi><mo>'</mo><mi>B</mi><mo>'</mo><mi>C</mi><mo>'</mo><mo>)</mo></math></p>
<p><strong>b)</strong> Những cặp mặt phẳng vuông góc với nhau: <math xmlns="http://www.w3.org/1998/Math/MathML"><mo>(</mo><mi>A</mi><mi>B</mi><mi>B</mi><mo>'</mo><mi>A</mi><mo>'</mo><mo>)</mo><mo> </mo><mo>⊥</mo><mo> </mo><mo>(</mo><mi>A</mi><mo>'</mo><mi>B</mi><mo>'</mo><mi>C</mi><mo>)</mo><mo>;</mo><mo> </mo><mo>(</mo><mi>A</mi><mi>C</mi><mi>C</mi><mo>'</mo><mi>A</mi><mo>'</mo><mo>)</mo><mo> </mo><mo>⊥</mo><mo> </mo><mo>(</mo><mi>A</mi><mo>'</mo><mi>B</mi><mo>'</mo><mi>C</mi><mo>'</mo><mo>)</mo><mo>;</mo><mo> </mo><mo>(</mo><mi>B</mi><mi>C</mi><mi>C</mi><mo>'</mo><mi>B</mi><mo>'</mo><mo>)</mo><mo> </mo><mo>⊥</mo><mo> </mo><mo>(</mo><mi>A</mi><mo>'</mo><mi>B</mi><mo>'</mo><mi>C</mi><mo>'</mo><mo>)</mo><mo>;</mo><mo> </mo><mo>(</mo><mi>A</mi><mi>B</mi><mi>B</mi><mo>'</mo><mi>A</mi><mo>'</mo><mo>)</mo><mo> </mo><mo>⊥</mo><mo> </mo><mo>(</mo><mi>A</mi><mi>B</mi><mi>C</mi><mo>)</mo><mo>;</mo><mo> </mo><mo>(</mo><mi>A</mi><mi>C</mi><mi>C</mi><mo>'</mo><mi>A</mi><mo>'</mo><mo>)</mo><mo> </mo><mo>⊥</mo><mo> </mo><mo>(</mo><mi>A</mi><mi>B</mi><mi>C</mi><mo>)</mo><mo>;</mo><mo> </mo><mo>(</mo><mi>B</mi><mi>C</mi><mi>C</mi><mo>'</mo><mi>B</mi><mo>'</mo><mo>)</mo><mo> </mo><mo>⊥</mo><mo> </mo><mo>(</mo><mi>A</mi><mi>B</mi><mi>C</mi><mo>)</mo></math></p>
<p><strong>c)</strong></p>
<table style="border-collapse: collapse; width: 102.16%; height: 126.141px;" border="1">
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<tr style="height: 50.1875px;">
<td style="width: 18.8559%; height: 50.1875px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac bevelled="true"><mrow><mi>C</mi><mi>ạ</mi><mi>n</mi><mi>h</mi></mrow><mrow><mi>M</mi><mi>ặ</mi><mi>t</mi></mrow></mfrac></math></td>
<td style="width: 10.5932%; height: 50.1875px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>A</mi><mi>A</mi><mo>'</mo></math></td>
<td style="width: 9.95763%; height: 50.1875px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>C</mi><mi>C</mi><mo>'</mo></math></td>
<td style="width: 9.5339%; height: 50.1875px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>B</mi><mi>B</mi><mo>'</mo></math></td>
<td style="width: 9.32203%; height: 50.1875px;"><span style="vertical-align: inherit;"><span style="vertical-align: inherit;">A'C'</span></span></td>
<td style="width: 8.26271%; height: 50.1875px;"><span style="vertical-align: inherit;"><span style="vertical-align: inherit;">B'C '</span></span></td>
<td style="width: 9.32203%; height: 50.1875px;"><span style="vertical-align: inherit;"><span style="vertical-align: inherit;">A'B '</span></span></td>
<td style="width: 8.05085%; height: 50.1875px;"><span style="vertical-align: inherit;"><span style="vertical-align: inherit;">AC</span></span></td>
<td style="width: 7.83898%; height: 50.1875px;"><span style="vertical-align: inherit;"><span style="vertical-align: inherit;">CB</span></span></td>
<td style="width: 8.26271%; height: 50.1875px;"><span style="vertical-align: inherit;"><span style="vertical-align: inherit;">AB</span></span></td>
</tr>
<tr style="height: 25.0938px;">
<td style="width: 18.8559%; height: 25.0938px;"><span style="vertical-align: inherit;"><span style="vertical-align: inherit;">ACB</span></span></td>
<td style="width: 10.5932%; height: 25.0938px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mo>⊥</mo></math></td>
<td style="width: 9.95763%; height: 25.0938px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mo>⊥</mo></math></td>
<td style="width: 9.5339%; height: 25.0938px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mo>⊥</mo></math></td>
<td style="width: 9.32203%; height: 25.0938px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mo>/</mo><mo>/</mo></math></td>
<td style="width: 8.26271%; height: 25.0938px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mo>/</mo><mo>/</mo></math></td>
<td style="width: 9.32203%; height: 25.0938px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mo>/</mo><mo>/</mo></math></td>
<td style="width: 8.05085%; height: 25.0938px;"> </td>
<td style="width: 7.83898%; height: 25.0938px;"> </td>
<td style="width: 8.26271%; height: 25.0938px;"> </td>
</tr>
<tr style="height: 25.7656px;">
<td style="width: 18.8559%; height: 25.7656px;"><span style="vertical-align: inherit;"><span style="vertical-align: inherit;"><span style="vertical-align: inherit;"><span style="vertical-align: inherit;">A'C'B'</span></span></span></span></td>
<td style="width: 10.5932%; height: 25.7656px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mo>⊥</mo></math></td>
<td style="width: 9.95763%; height: 25.7656px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mo>⊥</mo></math></td>
<td style="width: 9.5339%; height: 25.7656px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mo>⊥</mo></math></td>
<td style="width: 9.32203%; height: 25.7656px;"> </td>
<td style="width: 8.26271%; height: 25.7656px;"> </td>
<td style="width: 9.32203%; height: 25.7656px;"> </td>
<td style="width: 8.05085%; height: 25.7656px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mo>/</mo><mo>/</mo></math></td>
<td style="width: 7.83898%; height: 25.7656px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mo>/</mo><mo>/</mo></math></td>
<td style="width: 8.26271%; height: 25.7656px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mo>/</mo><mo>/</mo></math></td>
</tr>
<tr style="height: 25.0938px;">
<td style="width: 18.8559%; height: 25.0938px;"><span style="vertical-align: inherit;"><span style="vertical-align: inherit;">ABB'A'</span></span></td>
<td style="width: 10.5932%; height: 25.0938px;"> </td>
<td style="width: 9.95763%; height: 25.0938px;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mo>/</mo><mo>/</mo></math></td>
<td style="width: 9.5339%; height: 25.0938px;"> </td>
<td style="width: 9.32203%; height: 25.0938px;"> </td>
<td style="width: 8.26271%; height: 25.0938px;"> </td>
<td style="width: 9.32203%; height: 25.0938px;"> </td>
<td style="width: 8.05085%; height: 25.0938px;"> </td>
<td style="width: 7.83898%; height: 25.0938px;"> </td>
<td style="width: 8.26271%; height: 25.0938px;"> </td>
</tr>
</tbody>
</table>
<p> </p>
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