Bài 3: Bảng lượng giác
Hướng dẫn giải Bài 19 (Trang 84 SGK Toán Hình học 9, Tập 1)
<p><strong>B&agrave;i 19 (Trang 83, SGK To&aacute;n H&igrave;nh học 9, Tập 1):</strong></p> <p>D&ugrave;ng bảng lượng gi&aacute;c hoặc m&aacute;y t&iacute;nh bỏ t&uacute;i để t&igrave;m số đo của g&oacute;c nhọn x (l&agrave;m tr&ograve;n đến ph&uacute;t) biết rằng:</p> <p>a)&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>sin</mi><mo>&#160;</mo><mi mathvariant="normal">x</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>0</mn><mo>,</mo><mn>2368</mn></math></p> <p>b)&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>cos</mi><mo>&#160;</mo><mi mathvariant="normal">x</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>0</mn><mo>,</mo><mn>6224</mn></math></p> <p>c)&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>tg</mi><mo>&#160;</mo><mi mathvariant="normal">x</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>2</mn><mo>,</mo><mn>154</mn></math></p> <p>d)&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>cotg</mi><mo>&#160;</mo><mi mathvariant="normal">x</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>3</mn><mo>,</mo><mn>251</mn></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"><mi>sin</mi><mo>&#160;</mo><mi mathvariant="normal">x</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>0</mn><mo>,</mo><mn>2368</mn><mo>&#160;</mo><mo>&#8658;</mo><mo>&#160;</mo><mi mathvariant="normal">x</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>13</mn><mo>&#176;</mo><mn>42</mn><mo>'</mo></math></p> <p>b)&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>cos</mi><mo>&#160;</mo><mi mathvariant="normal">x</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>0</mn><mo>,</mo><mn>6224</mn><mo>&#160;</mo><mo>&#8658;</mo><mo>&#160;</mo><mi mathvariant="normal">x</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>51</mn><mo>&#176;</mo><mn>30</mn><mo>'</mo></math></p> <p>c)&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>tg</mi><mo>&#160;</mo><mi mathvariant="normal">x</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>2</mn><mo>,</mo><mn>154</mn><mo>&#160;</mo><mo>&#8658;</mo><mo>&#160;</mo><mi mathvariant="normal">x</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>65</mn><mo>&#176;</mo><mn>6</mn><mo>'</mo></math></p> <p>d)&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>cotg</mi><mo>&#160;</mo><mi mathvariant="normal">x</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>3</mn><mo>,</mo><mn>251</mn><mo>&#160;</mo><mo>&#8658;</mo><mo>&#160;</mo><mi mathvariant="normal">x</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>17</mn><mo>&#176;</mo><mn>6</mn><mo>'</mo></math></p>
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