Bài 3. Đạo hàm của hàm số lượng giác
Hướng dẫn giải Bài 2 (Trang 168 SGK Toán Đại số & Giải tích 11)
<p>Giải c&aacute;c bất phương tr&igrave;nh&nbsp;</p> <p><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>a</mi><mo>,</mo><mo>&#160;</mo><mi>y</mi><mo>'</mo><mo>&#60;</mo><mn>0</mn><mo>&#160;</mo><mi>v</mi><mi>&#7899;</mi><mi>i</mi><mo>&#160;</mo><mi>y</mi><mo>=</mo><mfrac><mrow><msup><mi>x</mi><mn>2</mn></msup><mo>+</mo><mi>x</mi><mo>+</mo><mn>2</mn></mrow><mrow><mi>x</mi><mo>-</mo><mn>1</mn></mrow></mfrac><mspace linebreak="newline"/><mi>b</mi><mo>,</mo><mo>&#160;</mo><mi>y</mi><mo>'</mo><mo>&#8805;</mo><mn>0</mn><mo>&#160;</mo><mi>v</mi><mi>&#7899;</mi><mi>i</mi><mo>&#160;</mo><mi>y</mi><mo>=</mo><mfrac><mrow><msup><mi>x</mi><mn>2</mn></msup><mo>+</mo><mn>3</mn></mrow><mrow><mi>x</mi><mo>+</mo><mn>1</mn></mrow></mfrac><mspace linebreak="newline"/><mi>c</mi><mo>,</mo><mo>&#160;</mo><mi>y</mi><mo>&#62;</mo><mn>0</mn><mo>&#160;</mo><mi>v</mi><mi>&#7899;</mi><mi>i</mi><mo>&#160;</mo><mi>y</mi><mo>'</mo><mo>=</mo><mfrac><mrow><mn>2</mn><mi>x</mi><mo>-</mo><mn>1</mn></mrow><mrow><msup><mi>x</mi><mn>2</mn></msup><mo>+</mo><mi>x</mi><mo>+</mo><mn>4</mn></mrow></mfrac><mspace linebreak="newline"/><mi>G</mi><mi>i</mi><mi>&#7843;</mi><mi>i</mi><mo>&#160;</mo><mspace linebreak="newline"/><mi>a</mi><mo>,</mo><mo>&#160;</mo><mspace linebreak="newline"/><mi>T</mi><mi>a</mi><mo>&#160;</mo><mi>c</mi><mi>&#243;</mi><mo>&#160;</mo><mi>y</mi><mo>'</mo><mo>=</mo><mfrac><mrow><mfenced><mrow><mn>2</mn><mi>x</mi><mo>+</mo><mn>1</mn></mrow></mfenced><mfenced><mrow><mi>x</mi><mo>-</mo><mn>1</mn></mrow></mfenced><mo>-</mo><mfenced><mrow><msup><mi>x</mi><mn>2</mn></msup><mo>+</mo><mi>x</mi><mo>+</mo><mn>2</mn></mrow></mfenced></mrow><msup><mfenced><mrow><mi>x</mi><mo>-</mo><mn>1</mn></mrow></mfenced><mn>2</mn></msup></mfrac><mo>=</mo><mfrac><mrow><msup><mi>x</mi><mn>2</mn></msup><mo>-</mo><mn>2</mn><mi>x</mi><mo>-</mo><mn>3</mn></mrow><msup><mfenced><mrow><mi>x</mi><mo>-</mo><mn>1</mn></mrow></mfenced><mn>2</mn></msup></mfrac><mspace linebreak="newline"/><mi>y</mi><mo>'</mo><mo>&#60;</mo><mn>0</mn><mo>&#8660;</mo><mfenced open="{" close=""><mtable columnalign="left"><mtr><mtd><msup><mi>x</mi><mn>2</mn></msup><mo>-</mo><mn>2</mn><mi>x</mi><mo>-</mo><mn>3</mn><mo>&#60;</mo><mn>0</mn></mtd></mtr><mtr><mtd><mi>x</mi><mo>&#8800;</mo><mn>1</mn></mtd></mtr></mtable></mfenced><mo>&#8660;</mo><mfenced open="{" close=""><mtable columnalign="left"><mtr><mtd><mo>-</mo><mn>1</mn><mo>&#60;</mo><mi>x</mi><mo>&#60;</mo><mn>3</mn></mtd></mtr><mtr><mtd><mi>x</mi><mo>&#8800;</mo><mn>1</mn></mtd></mtr></mtable></mfenced><mspace linebreak="newline"/><mi>T</mi><mi>&#7853;</mi><mi>p</mi><mo>&#160;</mo><mi>n</mi><mi>g</mi><mi>h</mi><mi>i</mi><mi>&#7879;</mi><mi>m</mi><mo>&#160;</mo><mi>b</mi><mi>&#7845;</mi><mi>t</mi><mo>&#160;</mo><mi>p</mi><mi>h</mi><mi>&#432;</mi><mi>&#417;</mi><mi>n</mi><mi>g</mi><mo>&#160;</mo><mi>t</mi><mi>r</mi><mi>&#236;</mi><mi>n</mi><mi>h</mi><mo>&#160;</mo><mi>y</mi><mo>'</mo><mo>&#60;</mo><mn>0</mn><mo>&#160;</mo><mi>l</mi><mi>&#224;</mi><mo>&#160;</mo><mi>S</mi><mo>=</mo><mfenced><mrow><mo>-</mo><mn>1</mn><mo>;</mo><mn>1</mn></mrow></mfenced><mo>&#8746;</mo><mfenced><mrow><mn>1</mn><mo>;</mo><mn>3</mn></mrow></mfenced><mspace linebreak="newline"/><mi>b</mi><mo>,</mo><mspace linebreak="newline"/><mi>y</mi><mo>'</mo><mo>=</mo><mfrac><mrow><mn>2</mn><mi>x</mi><mfenced><mrow><mi>x</mi><mo>+</mo><mn>1</mn></mrow></mfenced><mo>-</mo><mfenced><mrow><msup><mi>x</mi><mn>2</mn></msup><mo>+</mo><mn>3</mn></mrow></mfenced></mrow><msup><mfenced><mrow><mi>x</mi><mo>+</mo><mn>1</mn></mrow></mfenced><mn>2</mn></msup></mfrac><mo>=</mo><mfrac><mrow><msup><mi>x</mi><mn>2</mn></msup><mo>+</mo><mn>2</mn><mi>x</mi><mo>-</mo><mn>3</mn></mrow><msup><mfenced><mrow><mi>x</mi><mo>+</mo><mn>1</mn></mrow></mfenced><mn>2</mn></msup></mfrac><mspace linebreak="newline"/><mi>y</mi><mo>'</mo><mo>&#8805;</mo><mn>0</mn><mo>&#8660;</mo><mfenced open="{" close=""><mtable columnalign="left"><mtr><mtd><msup><mi>x</mi><mn>2</mn></msup><mo>+</mo><mn>2</mn><mi>x</mi><mo>-</mo><mn>3</mn></mtd></mtr><mtr><mtd><mi>x</mi><mo>&#8800;</mo><mo>-</mo><mn>1</mn></mtd></mtr></mtable></mfenced><mo>&#8660;</mo><mfenced open="{" close=""><mtable 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linebreak="newline"/><mi>y</mi><mo>'</mo><mo>=</mo><mfrac><mrow><mn>2</mn><mfenced><mrow><msup><mi>x</mi><mn>2</mn></msup><mo>+</mo><mi>x</mi><mo>+</mo><mn>4</mn></mrow></mfenced><mo>-</mo><mfenced><mrow><mn>2</mn><mi>x</mi><mo>+</mo><mn>1</mn></mrow></mfenced><mfenced><mrow><mn>2</mn><mi>x</mi><mo>-</mo><mn>1</mn></mrow></mfenced></mrow><msup><mfenced><mrow><msup><mi>x</mi><mn>4</mn></msup><mo>+</mo><mi>x</mi><mo>+</mo><mn>4</mn></mrow></mfenced><mn>2</mn></msup></mfrac><mo>=</mo><mfrac><mrow><mo>-</mo><mn>2</mn><msup><mi>x</mi><mn>2</mn></msup><mo>+</mo><mn>2</mn><mi>x</mi><mo>+</mo><mn>9</mn></mrow><msup><mfenced><mrow><msup><mi>x</mi><mn>2</mn></msup><mo>+</mo><mi>x</mi><mo>+</mo><mn>4</mn></mrow></mfenced><mn>2</mn></msup></mfrac><mspace linebreak="newline"/><mi>y</mi><mo>'</mo><mo>&#62;</mo><mn>0</mn><mo>&#8660;</mo><mo>-</mo><mn>2</mn><msup><mi>x</mi><mn>2</mn></msup><mo>+</mo><mi>x</mi><mo>+</mo><mn>9</mn><mo>&#62;</mo><mn>0</mn><mo>&#8660;</mo><mfrac><mrow><mn>1</mn><mo>-</mo><msqrt><mn>19</mn></msqrt></mrow><mn>2</mn></mfrac><mo>&#60;</mo><mi>x</mi><mo>&#60;</mo><mfrac><mrow><mn>1</mn><mo>+</mo><msqrt><mn>19</mn></msqrt></mrow><mn>2</mn></mfrac><mspace linebreak="newline"/><mi>V</mi><mi>&#7853;</mi><mi>y</mi><mo>&#160;</mo><mi>S</mi><mo>=</mo><mfenced><mrow><mfrac><mrow><mn>1</mn><mo>-</mo><msqrt><mn>19</mn></msqrt></mrow><mn>2</mn></mfrac><mo>;</mo><mfrac><mrow><mn>1</mn><mo>+</mo><msqrt><mn>19</mn></msqrt></mrow><mn>2</mn></mfrac></mrow></mfenced></math></p>
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