Tính góc tạo bởi hai đường thẳng d 1 : 6x – 5y + 15 = 0 và d 2 : x = 10 − 6 t y = 1 + 5 t A.   30 ° ;                   B. 45 ° ;           C. 60 ° ; D. 90 ° .

<p><div class=""></p><p> <div class=""></p><p> <div></p><p> <p class="" style="text-align: justify; mso-pagination: none; tab-stops: 0in 22.7pt 28.35pt 36.85pt 42.55pt 51.05pt 99.25pt 198.45pt 297.7pt right 396.9pt;"><strong><span style=" mso-ansi-language: NL;">Hướng dẫn giải</span></strong></p></p><p> <p class="" style="text-align: justify; mso-pagination: none; tab-stops: 0in 22.7pt 28.35pt 36.85pt 42.55pt 51.05pt 99.25pt 198.45pt 297.7pt right 396.9pt;"><strong><span style=" mso-ansi-language: NL;">Đáp án đúng là: D</span></strong></p></p><p> <p class="" style="text-align: justify; mso-pagination: none; tab-stops: 0in 22.7pt 28.35pt 36.85pt 42.55pt 51.05pt 99.25pt 198.45pt 297.7pt right 396.9pt;"><span style=" mso-ansi-language: NL; mso-bidi-font-weight: bold;">Đường thẳng d₁ có vectơ pháp tuyến&nbsp; <math><mover><msub><mi>n</mi><mn>1</mn></msub><mo>→</mo></mover><mo>(</mo><mn>6</mn><mo>;</mo><mo>−</mo><mn>5</mn><mo>)</mo></math><span style="position: relative; top: 6.0pt; mso-text-raise: -6.0pt;"></span></span></p></p><p> <p class="" style="text-align: justify; mso-pagination: none; tab-stops: 0in 22.7pt 28.35pt 36.85pt 42.55pt 51.05pt 99.25pt 198.45pt 297.7pt right 396.9pt;"><span style=" mso-ansi-language: NL; mso-bidi-font-weight: bold;">Đường thẳng d₂ có vectơ chỉ phương <math><mover><msub><mi>u</mi><mn>1</mn></msub><mo>→</mo></mover><mo>(</mo><mo>−</mo><mn>6</mn><mo>;</mo><mn>5</mn><mo>)</mo></math><span style="mso-spacerun: yes;">&nbsp;</span></span></p></p><p> <p class="" style="text-align: justify; mso-pagination: none; tab-stops: 0in 22.7pt 28.35pt 36.85pt 42.55pt 51.05pt 99.25pt 198.45pt 297.7pt right 396.9pt;"><span style=" mso-bidi- mso-ansi-language: NL; mso-bidi-font-weight: bold;">⇒</span><span style=" mso-ansi-language: NL; mso-bidi-font-weight: bold;"> vectơ pháp tuyến của d₂ là:&nbsp; <math><mover><msub><mi>n</mi><mn>2</mn></msub><mo>→</mo></mover><mo>(</mo><mn>5</mn><mo>;</mo><mn>6</mn><mo>)</mo></math><span style="position: relative; top: 6.0pt; mso-text-raise: -6.0pt;"></span></span></p></p><p> <p class="" style="text-align: justify; mso-pagination: none; tab-stops: 0in 22.7pt 28.35pt 36.85pt 42.55pt 51.05pt 99.25pt 198.45pt 297.7pt right 396.9pt;"><span style=" mso-ansi-language: NL; mso-bidi-font-weight: bold;">Ta có: <math><mover><msub><mi>n</mi><mn>1</mn></msub><mo>→</mo></mover><mo>.</mo><mover><msub><mi>n</mi><mn>2</mn></msub><mo>→</mo></mover></math><span style="mso-spacerun: yes;">&nbsp;</span>= 6.5 + (−5).6 = 0 nên <math><mover><msub><mi>n</mi><mn>1</mn></msub><mo>→</mo></mover></math><span style="mso-spacerun: yes;">&nbsp;</span>và <math><mover><msub><mi>n</mi><mn>2</mn></msub><mo>→</mo></mover></math><span style="mso-spacerun: yes;">&nbsp;</span>vuông góc với nhau</span></p></p><p> <p class="" style="text-align: justify; mso-pagination: none; tab-stops: 0in 22.7pt 28.35pt 36.85pt 42.55pt 51.05pt 99.25pt 198.45pt 297.7pt right 396.9pt;"><span style=" mso-ansi-language: NL; mso-bidi-font-weight: bold;">Hay hai đường thẳng d₁ và d₂ vuông góc với nhau.</span></p></p><p> <p class="" style="text-align: justify; mso-pagination: none; tab-stops: 0in 22.7pt 28.35pt 36.85pt 42.55pt 51.05pt 99.25pt 198.45pt 297.7pt right 396.9pt;"><span style=" mso-ansi-language: NL; mso-bidi-font-weight: bold;">Vậy góc giữa hai đường thẳng d₁ và d₂ là: </span><span style=" mso-ansi-language: NL;">90^°.</span></p></p><p> </div></p><p> </div> </p><p></div></p>