Đại lượng tỉ lệ nghịch - Bài tập trung bình

Home Toán lớp 7 - Sách KNTT Bài 23: Đại lượng tỉ lệ nghịchBài tập trung bình

{"common":{"save":0,"post_id":"5798","level":2,"total":10,"point":10,"point_extra":0},"segment":[{"id":"8304","post_id":"5798","mon_id":"1158532","chapter_id":"1158659","question":"Cho x t\u1ec9 l\u1ec7 thu\u1eadn v\u1edbi y và y t\u1ec9 l\u1ec7 thu\u1eadn v\u1edbi z. Khi \u0111ó m\u1ed1i quan h\u1ec7 gi\u1eefa hai \u0111\u1ea1i l\u01b0\u1ee3ng x và z là?<\/p>","options":["A. <\/strong>x và z t\u1ec9 l\u1ec7 ngh\u1ecbch v\u1edbi nhau","B. <\/strong>x và z t\u1ec9 l\u1ec7 thu\u1eadn v\u1edbi nhau","C. <\/strong>x và z không t\u1ec9 l\u1ec7 ngh\u1ecbch c\u0169ng không t\u1ec9 l\u1ec7 thu\u1eadn v\u1edbi nhau","D. <\/strong>Không xác \u0111\u1ecbnh \u0111\u01b0\u1ee3c"],"correct":"2","level":"2","hint":"","answer":"Gi\u1ea3 s\u1eed x t\u1ec9 l\u1ec7 thu\u1eadn v\u1edbi y theo h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7 m, suy ra x = m . y<\/span><\/p>            y t\u1ec9 l\u1ec7 thu\u1eadn v\u1edbi z theo h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7 n, suy ra y = n . z<\/span><\/p>Suy ra x = m . y = m . (n . z) hay x = (m.n) . z<\/span><\/p>Suy ra x t\u1ec9 l\u1ec7 thu\u1eadn v\u1edbi z theo h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7 là m.n.<\/p>V\u1eady \u0111áp án \u0111úng là B. <\/strong>x và z t\u1ec9 l\u1ec7 thu\u1eadn v\u1edbi nhau<\/span><\/p>","type":"choose","extra_type":"classic","time":"0","user_id":"131","test":"1","date":"2022-05-28 10:35:34","option_type":"txt","len":3},{"id":"8306","post_id":"5798","mon_id":"1158532","chapter_id":"1158659","question":"Cho x t\u1ec9 l\u1ec7 ngh\u1ecbch v\u1edbi y và y t\u1ec9 l\u1ec7 ngh\u1ecbch v\u1edbi z. Khi \u0111ó m\u1ed1i quan h\u1ec7 gi\u1eefa hai \u0111\u1ea1i l\u01b0\u1ee3ng x và z là?<\/p>","options":["A. <\/strong>x và z t\u1ec9 l\u1ec7 ngh\u1ecbch v\u1edbi nhau","B. <\/strong>x và z t\u1ec9 l\u1ec7 thu\u1eadn v\u1edbi nhau","C. <\/strong>x và z không t\u1ec9 l\u1ec7 ngh\u1ecbch c\u0169ng không t\u1ec9 l\u1ec7 thu\u1eadn v\u1edbi nhau","D. <\/strong>Không xác \u0111\u1ecbnh \u0111\u01b0\u1ee3c"],"correct":"2","level":"2","hint":"","answer":"Gi\u1ea3 s\u1eed x t\u1ec9 l\u1ec7 ngh\u1ecbch v\u1edbi y theo h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7 m, suy ra x = $\\dfrac{m}{y}$<\/span><\/span><\/p>            y t\u1ec9 l\u1ec7 ngh\u1ecbch v\u1edbi z theo h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7 n, suy ra y = $\\dfrac{n}{z}$<\/span><\/span><\/p>Suy ra x = $\\dfrac{m}{y}=m:y$<\/span> = $m:\\dfrac{n}{z}=m.\\dfrac{z}{n}=\\dfrac{m}{n}.z$<\/span> hay x = $\\dfrac{m}{n}.z$<\/span><\/span><\/p>Suy ra x t\u1ec9 l\u1ec7 thu\u1eadn v\u1edbi z theo h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7 là $\\dfrac{m}{n}$<\/span>.<\/p>V\u1eady \u0111áp án \u0111úng là B. <\/strong>x và z t\u1ec9 l\u1ec7 thu\u1eadn v\u1edbi nhau<\/span><\/p>","type":"choose","extra_type":"classic","time":"0","user_id":"131","test":"1","date":"2022-05-28 10:40:57","option_type":"txt","len":3},{"id":"8359","post_id":"5798","mon_id":"1158532","chapter_id":"1158659","question":"Cho x và y là hai \u0111\u1ea1i l\u01b0\u1ee3ng t\u1ec9 l\u1ec7 ngh\u1ecbch. \u0110i\u1ec1n các s\u1ed1 thích h\u1ee3p vào ô tr\u1ed1ng trong b\u1ea3ng sau:<\/p><table border=\"1\" cellpadding=\"1\" cellspacing=\"1\" style=\"width: 750px;\"><tbody> <tr> <td>x<\/strong><\/td> <td>5<\/td> <td>10<\/td> <td><input class=\"tim_x input_number\" tpl=\"dien_so\" type=\"text\"\/><\/td> <\/tr> <tr> <td>y<\/strong><\/td> <td>60<\/td> <td><input class=\"tim_x input_number\" tpl=\"dien_so\" type=\"text\"\/><\/td> <td>15<\/td> <\/tr><\/tbody><\/table>","options":"","correct":["[\"20\",\"30\"]"],"level":"2","hint":"N\u1ebfu hai \u0111\u1ea1i l\u01b0\u1ee3ng x và y t\u1ec9 l\u1ec7 ngh\u1ecbch v\u1edbi nhau thì tích hai giá tr\u1ecb t\u01b0\u01a1ng \u1ee9ng c\u1ee7a chúng luôn không \u0111\u1ed5i (và b\u1eb1ng h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7)<\/p>t\u1ee9c là $x_1.y_1=x_2.y_2=...=a$<\/span><\/p>","answer":"Gi\u1ea3 s\u1eed x và y t\u1ec9 l\u1ec7 ngh\u1ecbch v\u1edbi nhau theo h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7 $a$<\/span> ($a\\ne0$<\/span>).<\/p>Do \u0111ó $a = x_1.y_1=5.60 = 300$<\/span>. Suy ra $y=\\dfrac{300}{x}$<\/span><\/p>Khi $x_2 = 10$<\/span> thì $y_2=\\dfrac{300}{10}=30$<\/span><\/p>Khi $y_3 = 15$<\/span> thì $15=\\dfrac{300}{x_3}$<\/span> . Suy ra $x_3 = \\dfrac{300}{15}=20$<\/span><\/p>V\u1eady các s\u1ed1 c\u1ea7n \u0111i\u1ec1n l\u1ea7n l\u01b0\u1ee3t là 20  ;  30<\/span><\/p>","type":"blank","extra_type":"","time":"0","user_id":"131","test":"3","date":"2022-05-29 03:33:07"}]}