Đại lượng tỉ lệ thuận

Home Toán lớp 7 - Sách KNTT Bài 22: Đại lượng tỉ lệ thuậnBài tập nâng cao

{"common":{"save":0,"post_id":"5796","level":3,"total":10,"point":10,"point_extra":0},"segment":[{"id":"8364","post_id":"5796","mon_id":"1158532","chapter_id":"1158659","question":"N\u1ebfu y t\u1ec9 l\u1ec7 thu\u1eadn v\u1edbi x theo h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7 là 3 và z t\u1ec9 l\u1ec7 thu\u1eadn v\u1edbi y theo h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7 là 4 thì z có t\u1ec9 l\u1ec7 thu\u1eadn v\u1edbi x không? N\u1ebfu có thì h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7 là bao nhiêu?<\/p>","options":["A. <\/strong>Có, h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7 là 12","B.<\/strong> Có, h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7 là $\\dfrac{3}{4}$<\/span>","C.<\/strong> Có, h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7 là $\\dfrac{4}{3}$<\/span>","D. <\/strong>Không"],"correct":"1","level":"3","hint":"","answer":"Vì y t\u1ec9 l\u1ec7 thu\u1eadn v\u1edbi x theo h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7 là 3 nên y = 3x<\/p>Vì z t\u1ec9 l\u1ec7 thu\u1eadn v\u1edbi y theo h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7 là 4 nên z = 4y<\/p>Suy ra z = 4y = 4 . 3x = 12x<\/p>Do \u0111ó z t\u1ec9 l\u1ec7 thu\u1eadn v\u1edbi x theo h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7 là 12<\/p>\u0110áp án \u0111úng là   A. <\/strong>Có, h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7 là 12<\/span><\/p>","type":"choose","extra_type":"classic","time":"0","user_id":"131","test":"1","date":"2022-05-29 03:57:00","option_type":"math","len":0},{"id":"8366","post_id":"5796","mon_id":"1158532","chapter_id":"1158659","question":"Bi\u1ebft y t\u1ec9 l\u1ec7 thu\u1eadn v\u1edbi x theo h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7 là 5 và x t\u1ec9 l\u1ec7 thu\u1eadn v\u1edbi z theo h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7 là   $\\dfrac{2}{5}$<\/span> . H\u1ecfi y có t\u1ec9 l\u1ec7 thu\u1eadn v\u1edbi z không và n\u1ebfu có thì h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7 là bao nhiêu?<\/p>","options":["A. <\/strong>Không","B.<\/strong> Có, h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7 là 2","C. <\/strong>Có, h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7 là $\\dfrac{4}{5}$<\/span>","D.<\/strong> Có, h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7 là $\\dfrac{5}{2}$<\/span>"],"correct":"2","level":"3","hint":"","answer":"Vì y t\u1ec9 l\u1ec7 thu\u1eadn v\u1edbi x theo h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7 là 5 nên y = 5x<\/p>Vì x t\u1ec9 l\u1ec7 thu\u1eadn v\u1edbi z theo h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7 là   $\\dfrac{2}{5}$<\/span>  nên x = $\\dfrac{2}{5}$<\/span>z<\/p>Ta có: y = 5x = 5 . $\\dfrac{2}{5}$<\/span>z = 2z    hay y = 2z<\/p>V\u1eady y t\u1ec9 l\u1ec7 thu\u1eadn v\u1edbi z theo h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7 là 2<\/p>\u0110áp án \u0111úng là   B.<\/strong> Có, h\u1ec7 s\u1ed1 t\u1ec9 l\u1ec7 là  2<\/span><\/p>","type":"choose","extra_type":"classic","time":"0","user_id":"131","test":"1","date":"2022-05-29 04:06:53","option_type":"math","len":0},{"id":"8368","post_id":"5796","mon_id":"1158532","chapter_id":"1158659","question":"Hai b\u1ec3 n\u01b0\u1edbc hình h\u1ed9p ch\u1eef nh\u1eadt có chi\u1ec1u dài và chi\u1ec1u r\u1ed9ng t\u01b0\u01a1ng \u1ee9ng b\u1eb1ng nhau, nh\u01b0ng chi\u1ec1u cao c\u1ee7a b\u1ec3 th\u1ee9 nh\u1ea5t b\u1eb1ng $\\dfrac{4}{5}$<\/span> chi\u1ec1u cao c\u1ee7a b\u1ec3 th\u1ee9 hai. \u0110\u1ec3 b\u01a1m \u0111\u1ea7y n\u01b0\u1edbc vào b\u1ec3 th\u1ee9 nh\u1ea5t m\u1ea5t 4 gi\u1edd.  H\u1ecfi ph\u1ea3i m\u1ea5t bao lâu \u0111\u1ec3 b\u01a1m \u0111\u1ea7y n\u01b0\u1edbc vào b\u1ec3 th\u1ee9 hai (n\u1ebfu dùng máy b\u01a1m có cùng công su\u1ea5t)?<\/p>\u0110áp s\u1ed1: C\u1ea7n <input class=\"tim_x input_number\" tpl=\"dien_so\" type=\"text\"\/>  gi\u1edd \u0111\u1ec3 b\u01a1m \u0111\u1ea7y b\u1ec3 th\u1ee9 hai.<\/p>","options":"","correct":["[\"5\"]"],"level":"3","hint":"","answer":"G\u1ecdi  $t_1$<\/span> và $t_2$<\/span>  l\u1ea7n l\u01b0\u1ee3t là th\u1eddi gian b\u01a1m \u0111\u1ea7y n\u01b0\u1edbc c\u1ee7a b\u1ec3 th\u1ee9 nh\u1ea5t và b\u1ec3 th\u1ee9 hai ; $h_1$<\/span>  và  $h_2$<\/span>  l\u1ea7n l\u01b0\u1ee3t là chi\u1ec1u cao c\u1ee7a b\u1ec3 th\u1ee9 nh\u1ea5t và b\u1ec3 th\u1ee9 hai.<\/p>Vì hai b\u1ec3 n\u01b0\u1edbc có cùng chi\u1ec1u dài và chi\u1ec1u r\u1ed9ng và dùng máy b\u01a1m có công su\u1ea5t nh\u01b0 nhau nên chi\u1ec1u cao c\u1ee7a m\u1ed7i b\u1ec3 t\u1ec9 l\u1ec7 thu\u1eadn v\u1edbi th\u1eddi gian b\u01a1m n\u01b0\u1edbc.<\/p>Theo \u0111\u1ec1 bài ta có  $h_1 = \\dfrac{4}{5} . h_2$<\/span> , suy ra  $t_1 = \\dfrac{4}{5}.t_2$<\/span><\/p>Vì b\u01a1m \u0111\u1ea7y b\u1ec3 1 c\u1ea7n 4 gi\u1edd nên $t_1 = 4$<\/span><\/p>Suy ra 4 = $\\dfrac{4}{5}.t_2$<\/span> ⇒ $t_2=4:\\dfrac{4}{5}=4.\\dfrac{5}{4}$<\/span> = 5 gi\u1edd<\/p>S\u1ed1 c\u1ea7n \u0111i\u1ec1n là   5<\/span><\/p>","type":"blank","extra_type":"","time":"0","user_id":"131","test":"1","date":"2022-05-29 04:22:48"}]}