B\u00e0i 72 (trang 127 sgk Gi\u1ea3i T\u00edch 12 n\u00e2ng cao):<\/b>\u00a0<\/span><\/p>\nGi\u1ea3i c\u00e1c h\u1ec7 ph\u01b0\u01a1ng tr\u00ecnh:<\/p>\n
![\"\"](\"https:\/\/lop12.edu.vn\/wp-content\/uploads\/2018\/03\/1-403.png\")
<\/p>\n
L\u1eddi gi\u1ea3i:<\/b><\/p>\n
![\"\"](\"https:\/\/lop12.edu.vn\/wp-content\/uploads\/2018\/03\/2-261.png\")
<\/p>\n
\u0110i\u1ec1u ki\u1ec7n: x > 0; y > 0<\/p>\n
H\u1ec7 Ph\u01b0\u01a1ng tr\u00ecnh t\u01b0\u01a1ng d\u01b0\u01a1ng:<\/p>\n
![\"\"](\"https:\/\/lop12.edu.vn\/wp-content\/uploads\/2018\/03\/3-139.png\")
<\/p>\n
V\u1eady t\u1eadp nguy\u1ec7m c\u1ee7a h\u1ec7 Ph\u01b0\u01a1ng tr\u00ecnh l\u00e0 S={(2;18),(18;2)}<\/p>\n
![\"\"](\"https:\/\/lop12.edu.vn\/wp-content\/uploads\/2018\/03\/4-74.png\")
<\/p>\n
C\u00e1ch 1. R\u00fat y=1-x t\u1eeb Ph\u01b0\u01a1ng tr\u00ecnh \u0111\u1ea7u, th\u1ebf v\u00e0o Ph\u01b0\u01a1ng tr\u00ecnh th\u1ee9 hai \u0111\u01b0\u1ee3c:<\/p>\n
4-2x<\/sup>+4-2(1-x)<\/sup>=0,5 <=> (42x<\/sup>\u00a0)2-8.42x<\/sup>+16=0<\/p>\n\u0110\u1eb7t t=42x<\/sup>\u00a0(t > 0), ta \u0111\u01b0\u1ee3c t2<\/sup>-8t+16=0 <=> t = 4<\/p>\nV\u1edbi t = 4 => 42x<\/sup>=4 <=> 2x = 1 <=> x=1\/2 => y=1\/2<\/p>\nNghi\u1ec7m c\u1ee7a h\u1ec7 l\u00e0:<\/p>\n
![\"\"](\"https:\/\/lop12.edu.vn\/wp-content\/uploads\/2018\/03\/5-49.png\")
<\/p>\n
C\u00e1ch 2. x+y=1 <=> 4x+y<\/sup>=4 <=> 4x<\/sup>.4y<\/sup>=4<\/p>\n\u0110\u1eb7t u=4x<\/sup>,v=4y<\/sup>\u00a0ta \u0111\u01b0\u1ee3c:<\/p>\n![\"\"](\"https:\/\/lop12.edu.vn\/wp-content\/uploads\/2018\/03\/6-26.png\")
<\/p>\n
V\u00ec u > 0; v > 0<\/p>\n
=> T\u1eadp nghi\u1ec7m c\u1ee7a h\u1ec7 Ph\u01b0\u01a1ng tr\u00ecnh l\u00e0<\/p>\n
![\"\"](\"https:\/\/lop12.edu.vn\/wp-content\/uploads\/2018\/03\/7-17.png\")
<\/p>\n
B\u00e0i 73 (trang 127 sgk Gi\u1ea3i T\u00edch 12 n\u00e2ng cao):<\/b><\/span><\/p>\nGi\u1ea3i c\u00e1c h\u1ec7 ph\u01b0\u01a1ng tr\u00ecnh<\/p>\n
![\"\"](\"https:\/\/lop12.edu.vn\/wp-content\/uploads\/2018\/03\/1-404.png\")
<\/p>\n
L\u1eddi gi\u1ea3i:<\/b><\/p>\n
a) T\u1eeb Ph\u01b0\u01a1ng tr\u00ecnh th\u1ee9 hai ta suy ra: x+y=5 => y = 5 \u2013 x<\/p>\n
Th\u1ebf v\u00e0o Ph\u01b0\u01a1ng tr\u00ecnh \u0111\u00e2u ta \u0111\u01b0\u1ee3c:<\/p>\n
![\"\"](\"https:\/\/lop12.edu.vn\/wp-content\/uploads\/2018\/03\/2-262.png\")
<\/p>\n
V\u1eady h\u1ec7 Ph\u01b0\u01a1ng tr\u00ecnh c\u00f3 nghi\u1ec7m (x, y) l\u00e0 (-2; 7)<\/p>\n
![\"\"](\"https:\/\/lop12.edu.vn\/wp-content\/uploads\/2018\/03\/3-140.png\")
<\/p>\n
\u0110\u1eb7t u=log2<\/sub>(x+y) v\u00e0 v=log2<\/sub>(x-y)<\/p>\n![\"\"](\"https:\/\/lop12.edu.vn\/wp-content\/uploads\/2018\/03\/4-75.png\")
<\/p>\n
V\u1eady h\u1ec7 Ph\u01b0\u01a1ng tr\u00ecnh c\u00f3 nghi\u1ec7m (x; y) l\u00e0 (3\/2;1\/2)<\/p>\n","protected":false},"excerpt":{"rendered":"
B\u00e0i 72 (trang 127 sgk Gi\u1ea3i T\u00edch 12 n\u00e2ng cao):\u00a0 Gi\u1ea3i c\u00e1c h\u1ec7 ph\u01b0\u01a1ng tr\u00ecnh: L\u1eddi gi\u1ea3i: \u0110i\u1ec1u ki\u1ec7n: x > 0; y > 0 H\u1ec7 Ph\u01b0\u01a1ng tr\u00ecnh t\u01b0\u01a1ng d\u01b0\u01a1ng: V\u1eady t\u1eadp nguy\u1ec7m c\u1ee7a h\u1ec7 Ph\u01b0\u01a1ng tr\u00ecnh l\u00e0 S={(2;18),(18;2)} C\u00e1ch 1. R\u00fat y=1-x t\u1eeb Ph\u01b0\u01a1ng tr\u00ecnh \u0111\u1ea7u, th\u1ebf v\u00e0o Ph\u01b0\u01a1ng tr\u00ecnh th\u1ee9 hai \u0111\u01b0\u1ee3c: 4-2x+4-2(1-x)=0,5 […]<\/p>\n","protected":false},"author":3,"featured_media":23347,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_mi_skip_tracking":false,"tdm_status":"","tdm_grid_status":""},"categories":[1302],"tags":[1392,1393],"yoast_head":"\n
\u0110\u1ea1i s\u1ed1 - Ch\u01b0\u01a1ng 2 - B\u00e0i 8: H\u1ec7 ph\u01b0\u01a1ng tr\u00ecnh m\u0169 v\u00e0 l\u00f4garit<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/lop12.edu.vn\/dai-so-chuong-2-bai-8-he-phuong-trinh-mu-va-logarit\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"\u0110\u1ea1i s\u1ed1 - Ch\u01b0\u01a1ng 2 - B\u00e0i 8: H\u1ec7 ph\u01b0\u01a1ng tr\u00ecnh m\u0169 v\u00e0 l\u00f4garit\" \/>\n<meta property=\"og:description\" content=\"B\u00e0i 72 (trang 127 sgk Gi\u1ea3i T\u00edch 12 n\u00e2ng cao):\u00a0 Gi\u1ea3i c\u00e1c h\u1ec7 ph\u01b0\u01a1ng tr\u00ecnh: L\u1eddi gi\u1ea3i: \u0110i\u1ec1u ki\u1ec7n: x > 0; y > 0 H\u1ec7 Ph\u01b0\u01a1ng tr\u00ecnh t\u01b0\u01a1ng d\u01b0\u01a1ng: V\u1eady t\u1eadp nguy\u1ec7m c\u1ee7a h\u1ec7 Ph\u01b0\u01a1ng tr\u00ecnh l\u00e0 S={(2;18),(18;2)} C\u00e1ch 1. 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