Bài 4: Đường thẳng song song và đường thẳng cắt nhau
Hướng dẫn giải Bài 20 (Trang 54 SGK Toán 9, Tập 1)
<p><strong>B&agrave;i 20 (Trang 54 SGK To&aacute;n 9, Tập 1):</strong></p> <p>H&atilde;y chỉ ra ba cặp đường thẳng cắt nhau v&agrave; c&aacute;c cặp đường thẳng song song với nhau trong số c&aacute;c đường thẳng sau:</p> <p><math xmlns="http://www.w3.org/1998/Math/MathML"><mi mathvariant="normal">a</mi><mo>)</mo><mo>&#160;</mo><mi mathvariant="normal">y</mi><mo>=</mo><mn>1</mn><mo>,</mo><mn>5</mn><mi mathvariant="normal">x</mi><mo>+</mo><mn>2</mn><mo>;</mo><mspace linebreak="newline"/><mspace linebreak="newline"/><mi mathvariant="normal">b</mi><mo>)</mo><mo>&#160;</mo><mi mathvariant="normal">y</mi><mo>=</mo><mi mathvariant="normal">x</mi><mo>+</mo><mn>2</mn><mo>;</mo><mspace linebreak="newline"/><mspace linebreak="newline"/><mi mathvariant="normal">c</mi><mo>)</mo><mo>&#160;</mo><mi mathvariant="normal">y</mi><mo>=</mo><mn>0</mn><mo>,</mo><mn>5</mn><mi mathvariant="normal">x</mi><mo>-</mo><mn>3</mn><mo>;</mo><mspace linebreak="newline"/><mspace linebreak="newline"/><mi mathvariant="normal">d</mi><mo>)</mo><mo>&#160;</mo><mi mathvariant="normal">y</mi><mo>=</mo><mi mathvariant="normal">x</mi><mo>-</mo><mn>3</mn><mo>;</mo><mspace linebreak="newline"/><mspace linebreak="newline"/><mi mathvariant="normal">e</mi><mo>)</mo><mo>&#160;</mo><mi mathvariant="normal">y</mi><mo>=</mo><mn>1</mn><mo>,</mo><mn>5</mn><mi mathvariant="normal">x</mi><mo>-</mo><mn>1</mn><mo>;</mo><mspace linebreak="newline"/><mspace linebreak="newline"/><mi mathvariant="normal">g</mi><mo>)</mo><mo>&#160;</mo><mi mathvariant="normal">y</mi><mo>=</mo><mn>0</mn><mo>,</mo><mn>5</mn><mi mathvariant="normal">x</mi><mo>+</mo><mn>3</mn><mo>.</mo></math> &nbsp;</p> <p>&nbsp;</p> <p><strong><span style="text-decoration: underline;"><em>Hướng dẫn giải:</em></span></strong></p> <p>Hai đường thẳng cắt nhau l&agrave; hai đường thẳng c&oacute;&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>a</mi><mo>&#8800;</mo><mi>a</mi><mo>'</mo></math>. Ta c&oacute; ba cặp đường thẳng cắt nhau sau:</p> <p><math xmlns="http://www.w3.org/1998/Math/MathML"><mn>1</mn><mo>)</mo><mo>&#160;</mo><mi>y</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>1</mn><mo>,</mo><mn>5</mn><mi>x</mi><mo>&#160;</mo><mo>+</mo><mo>&#160;</mo><mn>2</mn><mo>&#160;</mo><mi>v</mi><mi>&#224;</mi><mo>&#160;</mo><mi>y</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mi>x</mi><mo>&#160;</mo><mo>+</mo><mo>&#160;</mo><mn>2</mn></math></p> <p><math xmlns="http://www.w3.org/1998/Math/MathML"><mn>2</mn><mo>)</mo><mo>&#160;</mo><mi mathvariant="normal">y</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>1</mn><mo>,</mo><mn>5</mn><mi mathvariant="normal">x</mi><mo>&#160;</mo><mo>+</mo><mo>&#160;</mo><mn>2</mn><mo>&#160;</mo><mo>&#160;</mo><mi>v&#224;</mi><mo>&#160;</mo><mi mathvariant="normal">y</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>0</mn><mo>,</mo><mn>5</mn><mi mathvariant="normal">x</mi><mo>&#160;</mo><mo>-</mo><mo>&#160;</mo><mn>3</mn></math></p> <p><math xmlns="http://www.w3.org/1998/Math/MathML"><mn>3</mn><mo>)</mo><mo>&#160;</mo><mi mathvariant="normal">y</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>1</mn><mo>,</mo><mn>5</mn><mi mathvariant="normal">x</mi><mo>&#160;</mo><mo>+</mo><mo>&#160;</mo><mn>2</mn><mo>&#160;</mo><mi>v&#224;</mi><mo>&#160;</mo><mi mathvariant="normal">y</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mi mathvariant="normal">x</mi><mo>&#160;</mo><mo>-</mo><mo>&#160;</mo><mn>3</mn></math>.</p> <p>Hai đường thẳng song song l&agrave; hai đường thẳng c&oacute;&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>a</mi><mo>=</mo><mi>a</mi><mo>'</mo></math> v&agrave; <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>b</mi><mo>&#8800;</mo><mi>b</mi><mo>'</mo></math>. Ta c&oacute; ba cặp đường thẳng song song sau:</p> <p><math xmlns="http://www.w3.org/1998/Math/MathML"><mn>1</mn><mo>)</mo><mo>&#160;</mo><mi mathvariant="normal">y</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>1</mn><mo>,</mo><mn>5</mn><mi mathvariant="normal">x</mi><mo>&#160;</mo><mo>+</mo><mo>&#160;</mo><mn>2</mn><mo>&#160;</mo><mi>v&#224;</mi><mo>&#160;</mo><mi mathvariant="normal">y</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>1</mn><mo>,</mo><mn>5</mn><mi mathvariant="normal">x</mi><mo>&#160;</mo><mo>-</mo><mo>&#160;</mo><mn>1</mn></math></p> <p><math xmlns="http://www.w3.org/1998/Math/MathML"><mn>2</mn><mo>)</mo><mo>&#160;</mo><mi mathvariant="normal">y</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mi mathvariant="normal">x</mi><mo>&#160;</mo><mo>+</mo><mo>&#160;</mo><mn>2</mn><mo>&#160;</mo><mi>v&#224;</mi><mo>&#160;</mo><mi mathvariant="normal">y</mi><mo>&#160;</mo><mo>=</mo><mi mathvariant="normal">x</mi><mo>&#160;</mo><mo>-</mo><mo>&#160;</mo><mn>3</mn></math> v&agrave;&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>y</mi><mo>=</mo><mi>x</mi><mo>-</mo><mn>3</mn></math></p> <p><math xmlns="http://www.w3.org/1998/Math/MathML"><mn>3</mn><mo>)</mo><mo>&#160;</mo><mi mathvariant="normal">y</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>0</mn><mo>,</mo><mn>5</mn><mi mathvariant="normal">x</mi><mo>&#160;</mo><mo>+</mo><mo>&#160;</mo><mn>3</mn><mo>&#160;</mo><mi>v&#224;</mi><mo>&#160;</mo><mi mathvariant="normal">y</mi><mo>&#160;</mo><mo>=</mo><mo>&#160;</mo><mn>0</mn><mo>,</mo><mn>5</mn><mi mathvariant="normal">x</mi><mo>&#160;</mo><mo>-</mo><mo>&#160;</mo><mn>3</mn><mo>.</mo></math></p>
Hướng dẫn Giải Bài 20 (trang 54, SGK Toán 9, Tập 1)
GV: GV colearn
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Hướng dẫn Giải Bài 20 (trang 54, SGK Toán 9, Tập 1)
GV: GV colearn