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Hướng dẫn giải Bài 38 (Trang 129 SGK Toán 9 Hình học, Tập 2)
<p>Thể t&iacute;ch phần cần t&iacute;nh gồm:</p> <p>- Thể t&iacute;ch h&igrave;nh trụ (một đ&aacute;y) đường k&iacute;nh đ&aacute;y 11cm, chiều cao 2 cm (<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>V</mi><mn>1</mn></msub></math>)</p> <p>- Thể t&iacute;ch h&igrave;nh trụ (một đ&aacute;y) đường k&iacute;nh đ&aacute;y 6 cm, chiều cao 7 cm (<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>V</mi><mn>2</mn></msub></math>) &nbsp;</p> <p>Ta c&oacute;:&nbsp; &nbsp; &nbsp; &nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>V</mi><mn>1</mn></msub></math> =&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">&#960;</mi><mo>&#160;</mo><msup><mfenced><mfrac><mn>11</mn><mn>2</mn></mfrac></mfenced><msup><mn>2</mn><mrow/></msup></msup><mo>.</mo><mo>&#160;</mo><mn>2</mn><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>3</mn><mo>,</mo><mn>14</mn><mo>&#160;</mo><mo>.</mo><mo>&#160;</mo><mfrac><mn>121</mn><mn>4</mn></mfrac><mo>&#160;</mo><mo>.</mo><mo>&#160;</mo><mn>2</mn><mo>&#160;</mo></math>&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mo>&#8776;</mo><mo>&#160;</mo><mn>189</mn><mo>,</mo><mn>97</mn><mo>&#160;</mo></math>(<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>c</mi><msup><mi>m</mi><mn>3</mn></msup></math>)</p> <p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>V</mi><mn>2</mn></msub></math> =&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">&#960;</mi></math>&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mfenced><mfrac><mn>6</mn><mn>2</mn></mfrac></mfenced><mn>2</mn></msup></math> . 7 = 3,14 .&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>36</mn><mn>4</mn></mfrac></math> . 7&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mo>&#8776;</mo></math> 197,82 (<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>c</mi><msup><mi>m</mi><mn>3</mn></msup></math>)</p> <p>Vậy thể t&iacute;ch của chi tiết m&aacute;y l&agrave;:&nbsp;</p> <p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; V =&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>V</mi><mn>1</mn></msub></math> +&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>V</mi><mn>2</mn></msub></math> = 189,97 + 197,82 = 387,79 (<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>c</mi><msup><mi>m</mi><mn>3</mn></msup></math>)</p> <p>Diện t&iacute;ch cần t&iacute;nh gồm:</p> <p>Diện t&iacute;ch xung quanh h&igrave;nh trụ c&oacute; đường k&iacute;nh đ&aacute;y 11 cm, chiều cao 2 cm:</p> <p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>S</mi><mn>1</mn></msub></math> = 2<math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">&#960;</mi></math>&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced><mfrac><mn>11</mn><mn>2</mn></mfrac></mfenced></math> . 2&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mo>&#8776;</mo></math> 69,08 (<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>c</mi><msup><mi>m</mi><mn>2</mn></msup></math>)</p> <p>Diện t&iacute;ch h&igrave;nh tr&ograve;n đ&aacute;y c&oacute; đường k&iacute;nh 11 cm:</p> <p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>S</mi><mn>2</mn></msub></math> =&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">&#960;</mi></math>&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mfenced><mfrac><mn>11</mn><mn>2</mn></mfrac></mfenced><mn>2</mn></msup></math>&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mo>&#8776;</mo></math>94,99 (<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>c</mi><msup><mi>m</mi><mn>2</mn></msup></math>)</p> <p>Diện t&iacute;ch một phần h&igrave;nh tr&ograve;n l&agrave; hiệu giữa diện t&iacute;ch h&igrave;nh tr&ograve;n đường k&iacute;nh 11cm v&agrave; diện t&iacute;ch h&igrave;nh tr&ograve;n đường k&iacute;nh 6 cm.</p> <p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>S</mi><mn>3</mn></msub></math> =&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">&#960;</mi></math>&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mfenced><mfrac><mn>11</mn><mn>2</mn></mfrac></mfenced><mn>2</mn></msup></math> -&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">&#960;</mi></math>&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mfenced><mfrac><mn>6</mn><mn>2</mn></mfrac></mfenced><mn>2</mn></msup></math> = 3,14 (&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mn>5</mn><mo>,</mo><msup><mn>5</mn><mn>2</mn></msup></math> -&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mn>3</mn><mn>2</mn></msup></math> )&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mo>&#8776;</mo></math> 66,73 (<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>c</mi><msup><mi>m</mi><mn>3</mn></msup></math>)</p> <p>Diện t&iacute;ch xung quanh h&igrave;nh trụ đường k&iacute;nh 6 cm, chiều cao 7 cm.</p> <p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>S</mi><mn>4</mn></msub></math> = 2<math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">&#960;</mi></math>&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced><mfrac><mn>6</mn><mn>2</mn></mfrac></mfenced></math> . 7 = 2 . 3,14 . 3 .7&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mo>&#8776;</mo></math> 131,88 (<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>c</mi><msup><mi>m</mi><mn>2</mn></msup></math>)</p> <p>Diện t&iacute;ch h&igrave;nh tr&ograve;n đ&aacute;y c&oacute; đường k&iacute;nh 6 cm:</p> <p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>S</mi><mn>5</mn></msub></math> =&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">&#960;</mi></math>&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mfenced><mfrac><mn>6</mn><mn>2</mn></mfrac></mfenced><mn>2</mn></msup></math> = 3,14 .&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mn>3</mn><mn>2</mn></msup></math>&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mo>&#8776;</mo></math> 28,26 (<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>c</mi><msup><mi>m</mi><mn>2</mn></msup></math>)</p> <p>Vậy diện t&iacute;ch bề mặt của chi tiết m&aacute;y l&agrave;:&nbsp;</p> <p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; S =&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>S</mi><mn>1</mn></msub><mo>&#160;</mo><mo>+</mo><mo>&#160;</mo><msub><mi>S</mi><mrow><mn>2</mn><mo>&#160;</mo></mrow></msub><mo>&#160;</mo><mo>+</mo><mo>&#160;</mo><msub><mi>S</mi><mn>3</mn></msub><mo>&#160;</mo><mo>+</mo><mo>&#160;</mo><msub><mi>S</mi><mn>4</mn></msub><mo>&#160;</mo><mo>+</mo><mo>&#160;</mo><msub><mi>S</mi><mn>5</mn></msub></math> = 390,94 (<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>c</mi><msup><mi>m</mi><mn>2</mn></msup></math>)</p> <p>&nbsp;</p> <p>&nbsp;</p>
Hướng dẫn Giải Bài 38 (Trang 129, SGK Toán Hình học 9, Tập 2)
GV: GV colearn
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Hướng dẫn Giải Bài 38 (Trang 129, SGK Toán Hình học 9, Tập 2)
GV: GV colearn