Bài 3: Liên hệ giữa phép nhân và phép khai phương
Hướng dẫn giải Bài 26 (Trang 16 SGK Toán 9, Tập 1)
<p><strong>B&agrave;i 26 (Trang 16 SGK To&aacute;n 9, Tập 1):</strong></p> <p><math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">a</mi><mo>)</mo><mo>&#160;</mo><mi>So</mi><mo>&#160;</mo><mi>s&#225;nh</mi><mo>&#160;</mo><msqrt><mn>25</mn><mo>+</mo><mn>9</mn></msqrt><mo>&#160;</mo><mi>v&#224;</mi><mo>&#160;</mo><msqrt><mn>25</mn></msqrt><mo>+</mo><msqrt><mn>9</mn></msqrt><mo>;</mo><mspace linebreak="newline"/><mspace linebreak="newline"/><mi mathvariant="normal">b</mi><mo>)</mo><mo>&#160;</mo><mi>V&#7899;i</mi><mo>&#160;</mo><mi mathvariant="normal">a</mi><mo>&#62;</mo><mn>0</mn><mo>&#160;</mo><mi>v&#224;</mi><mo>&#160;</mo><mi mathvariant="normal">b</mi><mo>&#62;</mo><mn>0</mn><mo>,</mo><mo>&#160;</mo><mi>ch&#7913;ng</mi><mo>&#160;</mo><mi>minh</mi><mo>&#160;</mo><msqrt><mfenced><mrow><mi mathvariant="normal">a</mi><mo>=</mo><mi mathvariant="normal">b</mi></mrow></mfenced></msqrt><mo>&#60;</mo><msqrt><mi mathvariant="normal">a</mi></msqrt><mo>+</mo><msqrt><mi mathvariant="normal">b</mi></msqrt></math></p> <p>&nbsp;</p> <p><strong><span style="text-decoration: underline;"><em>Hướng dẫn giải:</em></span></strong></p> <p><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>a</mi><mo>)</mo><mo>&#160;</mo><msqrt><mn>25</mn></msqrt><mo>&#160;</mo><mo>+</mo><mo>&#160;</mo><msqrt><mn>9</mn></msqrt><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>5</mn><mo>+</mo><mn>3</mn><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>8</mn><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><msqrt><mn>64</mn></msqrt><mo>&#160;</mo><mo>&#62;</mo><mo>&#160;</mo><msqrt><mn>34</mn></msqrt><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><msqrt><mn>25</mn><mo>+</mo><mn>9</mn></msqrt><mspace linebreak="newline"/><mspace linebreak="newline"/><mi>b</mi><mo>)</mo><mo>&#160;</mo><msqrt><mi>a</mi><mo>+</mo><mi>b</mi></msqrt><mo>&#160;</mo><mo>&#60;</mo><mo>&#160;</mo><msqrt><mi>a</mi></msqrt><mo>&#160;</mo><mo>+</mo><mo>&#160;</mo><msqrt><mi>b</mi></msqrt><mo>&#160;</mo><mo>&#8660;</mo><mo>&#160;</mo><msup><mrow><mo>(</mo><msqrt><mi>a</mi><mo>+</mo><mi>b</mi></msqrt><mo>)</mo></mrow><mn>2</mn></msup><mo>&#160;</mo><mo>&#60;</mo><mo>&#160;</mo><msup><mfenced><mrow><msqrt><mi>a</mi></msqrt><mo>+</mo><msqrt><mi>b</mi></msqrt></mrow></mfenced><mn>2</mn></msup><mspace linebreak="newline"/><mspace linebreak="newline"/><mo>&#8660;</mo><mi>a</mi><mo>&#160;</mo><mo>+</mo><mo>&#160;</mo><mi>b</mi><mo>&#160;</mo><mo>&#60;</mo><mo>&#160;</mo><mi>a</mi><mo>&#160;</mo><mo>+</mo><mo>&#160;</mo><mn>2</mn><msqrt><mi>a</mi><mi>b</mi></msqrt><mo>&#160;</mo><mo>+</mo><mo>&#160;</mo><mi>b</mi><mspace linebreak="newline"/><mspace linebreak="newline"/><mo>&#8660;</mo><mo>&#160;</mo><mn>0</mn><mo>&#160;</mo><mo>&#60;</mo><mo>&#160;</mo><mn>2</mn><msqrt><mi>a</mi><mi>b</mi></msqrt><mo>&#160;</mo><mfenced><mrow><mi>B</mi><mi>&#272;</mi><mi>T</mi><mo>&#160;</mo><mi>&#273;</mi><mi>&#250;</mi><mi>n</mi><mi>g</mi></mrow></mfenced><mspace linebreak="newline"/><mspace linebreak="newline"/><mi>V</mi><mi>&#7853;</mi><mi>y</mi><mo>&#160;</mo><msqrt><mi>a</mi><mo>+</mo><mi>b</mi></msqrt><mo>&#160;</mo><mo>&#60;</mo><mo>&#160;</mo><msqrt><mi>a</mi></msqrt><mo>&#160;</mo><mo>+</mo><mo>&#160;</mo><msqrt><mi>b</mi></msqrt></math></p>
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