Bài 1: Căn bậc hai
Hướng dẫn giải Bài 4 (Trang 7 SGK Toán 9, Tập 1)
<p><strong>B&agrave;i 4 (Trang 7, SGK To&aacute;n 9, Tập 1):</strong></p> <p>T&igrave;m x kh&ocirc;ng &acirc;m biết:</p> <p>a)<math xmlns="http://www.w3.org/1998/Math/MathML"><msqrt><mi>x</mi></msqrt><mo>&#160;</mo><mo>=</mo><mn>15</mn></math>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>b</mi><mo>)</mo><mo>&#160;</mo><mn>2</mn><msqrt><mi>x</mi></msqrt><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>14</mn></math></p> <p>c)<math xmlns="http://www.w3.org/1998/Math/MathML"><msqrt><mi>x</mi></msqrt><mo>&#60;</mo><msqrt><mn>2</mn></msqrt></math>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; d)<math xmlns="http://www.w3.org/1998/Math/MathML"><msqrt><mn>2</mn><mi>x</mi></msqrt><mo>&#160;</mo><mo>&#60;</mo><mn>4</mn></math></p> <p>&nbsp;</p> <p><strong><span style="text-decoration: underline;"><em>Hướng dẫn giải:</em></span></strong></p> <p>a) Ta c&oacute;: <math xmlns="http://www.w3.org/1998/Math/MathML"><msqrt><mi>x</mi></msqrt><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>15</mn><mo>&#160;</mo><mo>&#8660;</mo><msup><mi>x</mi><mn>2</mn></msup><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><msup><mn>15</mn><mn>2</mn></msup><mo>&#160;</mo><mo>&#8660;</mo><mi>x</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>225</mn><mo>.</mo></math></p> <p>Vậy x = 225</p> <p>b)<math xmlns="http://www.w3.org/1998/Math/MathML"><mn>2</mn><msqrt><mi>x</mi></msqrt><mo>&#160;</mo><mo>=</mo><mn>14</mn><mo>&#160;</mo><mo>&#8660;</mo><msqrt><mi>x</mi></msqrt><mo>&#160;</mo><mo>=</mo><mn>7</mn><mo>&#160;</mo><mo>&#8660;</mo><mi>x</mi><mo>=</mo><mn>49</mn></math></p> <p>Vậy x =&nbsp; 49</p> <p>c)&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msqrt><mi>x</mi></msqrt><mo>&#160;</mo><mo>&#60;</mo><mo>&#160;</mo><msqrt><mn>2</mn></msqrt><mo>&#8660;</mo><mi>x</mi><mo>&#160;</mo><mo>&#60;</mo><mo>&#160;</mo><mn>2</mn></math></p> <p>Vậy x &lt; 2</p> <p>d) V&igrave; <math xmlns="http://www.w3.org/1998/Math/MathML"><mn>4</mn><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><msqrt><mn>16</mn></msqrt></math> n&ecirc;n <math xmlns="http://www.w3.org/1998/Math/MathML"><mn>2</mn><msqrt><mi>x</mi></msqrt><mo>&#160;</mo><mo>&#60;</mo><mo>&#160;</mo><mn>4</mn></math> c&oacute; nghĩa l&agrave; <math xmlns="http://www.w3.org/1998/Math/MathML"><msqrt><mn>2</mn><mi>x</mi></msqrt><mo>&#160;</mo><mo>&#60;</mo><mo>&#160;</mo><msqrt><mn>16</mn></msqrt><mo>&#160;</mo><mo>&#8660;</mo><mn>2</mn><mi>x</mi><mo>&#160;</mo><mo>&#60;</mo><mo>&#160;</mo><mn>16</mn><mo>&#160;</mo><mo>&#8660;</mo><mo>&#160;</mo><mi>x</mi><mo>&#160;</mo><mo>&#60;</mo><mo>&#160;</mo><mn>8</mn><mo>&#160;</mo><mo>(</mo><mi>x</mi><mo>&#8805;</mo><mn>0</mn><mo>)</mo></math></p> <p>Vậy 0<math xmlns="http://www.w3.org/1998/Math/MathML"><mo>&#8804;</mo></math> x &lt; 8.</p>
Hướng dẫn Giải Bài 4 (trang 7, SGK Toán 9, Tập 1)
GV: GV colearn
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Hướng dẫn Giải Bài 4 (trang 7, SGK Toán 9, Tập 1)
GV: GV colearn