B\u00e0i 1 (trang 18 SGK H\u00ecnh h\u1ecdc 12):\u00a0C\u1eaft b\u00eca theo m\u1eabu d\u01b0\u1edbi \u0111\u00e2y (h.123), g\u1ea5p theo \u0111\u01b0\u1eddng k\u1ebb, r\u1ed3i d\u00e1n c\u00e1c m\u00e9p l\u1ea1i \u0111\u1ec3 \u0111\u01b0\u1ee3c c\u00e1c h\u00ecnh t\u1ee9 di\u1ec7n \u0111\u1ec1u, h\u00ecnh l\u1eadp ph\u01b0\u01a1ng v\u00e0 h\u00ecnh b\u00e1t di\u1ec7n \u0111\u1ec1u.<\/strong><\/span><\/p>\n L\u1eddi gi\u1ea3i:<\/b><\/p>\n C\u00e1c b\u1ea1n h\u1ecdc sinh t\u1ef1 th\u1ef1c hi\u1ec7n.<\/p>\n B\u00e0i 2 (trang 18 SGK H\u00ecnh h\u1ecdc 12):\u00a0Cho h\u00ecnh l\u1eadp ph\u01b0\u01a1ng (H). G\u1ecdi (H\u2019) l\u00e0 h\u00ecnh b\u00e1t di\u1ec7n \u0111\u1ec1u c\u00f3 c\u00e1c \u0111\u1ec9nh l\u00e0 t\u00e2m c\u00e1c m\u1eb7t c\u1ee7a (H). T\u00ednh t\u1ec9 s\u1ed1 di\u1ec7n t\u00edch to\u00e0n ph\u1ea7n c\u1ee7a (H) v\u00e0 (H\u2019).<\/strong><\/span><\/p>\n L\u1eddi gi\u1ea3i:<\/b><\/p>\n G\u1ecdi a l\u00e0 c\u1ea1nh c\u1ee7a h\u00ecnh l\u1eadp ph\u01b0\u01a1ng ABCD.A1<\/sub>B1<\/sub>C1<\/sub>D1<\/sub>; O1<\/sub>, O2<\/sub>\u00a0l\u1ea7n l\u01b0\u1ee3t l\u00e0 t\u00e2m c\u1ee7a ABCD v\u00e0 ABB1<\/sub>A1<\/sub>. Khi \u0111\u00f3 O1<\/sub>O2<\/sub>\u00a0l\u00e0 \u0111\u01b0\u1eddng trung b\u00ecnh c\u1ee7a tam gi\u00e1c A1<\/sub>BD.<\/p>\n Suy ra O1<\/sub>O2<\/sub>\u00a0=A1<\/sub>D\/2 = a\u221a2\/2<\/p>\n T\u1eeb \u0111\u00f3 ta c\u00f3: \u0110o\u1ea1n th\u1eb3ng n\u1ed1i hai t\u00e2m c\u1ee7a hai m\u1eb7t c\u00f3 chung m\u1ed9t c\u1ea1nh c\u1ee7a h\u00ecnh l\u1eadp ph\u01b0\u01a1ng th\u00ec c\u00f3 \u0111\u1ed9 d\u00e0i b\u1eb1ng a\u221a2\/2 .<\/p>\n V\u1eady s\u00e1u t\u00e2m c\u1ee7a s\u00e1u m\u1eb7t c\u1ee7a h\u00ecnh l\u1eadp ph\u01b0\u01a1ng t\u1ea1o th\u00e0nh t\u00e1m tam gi\u00e1c \u0111\u1ec1u c\u1ea1nh a\u221a2\/2 , m\u1ed7i t\u00e2m l\u00e0 \u0111\u1ec9nh chung c\u1ee7a \u0111\u00fang b\u1ed1n tam gi\u00e1c \u0111\u1ec1u, v\u00e0 t\u00e1m tam gi\u00e1c \u0111\u1ec1u n\u00e0y l\u00e0 t\u00e1m m\u1eb7t c\u1ee7a h\u00ecnh t\u00e1m m\u1eb7t \u0111\u1ec1u c\u1ea1nh b\u1eb1ng a\u221a2\/2 .<\/p>\n Di\u1ec7n t\u00edch to\u00e0n ph\u1ea7n c\u1ee7a h\u00ecnh l\u1eadp ph\u01b0\u01a1ng l\u00e0 S1<\/sub>\u00a0= 6a2<\/sup>.<\/p>\n Di\u1ec7n t\u00edch to\u00e0n ph\u1ea7n c\u1ee7a h\u00ecnh b\u00e1t di\u1ec7n \u0111\u1ec1u l\u00e0:<\/p>\n <\/p>\n B\u00e0i 3 (trang 18 SGK H\u00ecnh h\u1ecdc 12):\u00a0Ch\u1ee9ng minh r\u1eb1ng t\u00e2m c\u1ee7a c\u00e1c m\u1eb7t c\u1ee7a h\u00ecnh t\u1ee9 di\u1ec7n \u0111\u1ec1u l\u00e0 c\u00e1c \u0111\u1ec9nh c\u1ee7a m\u1ed9t t\u1ee9 di\u1ec7n \u0111\u1ec1u.<\/strong><\/span><\/p>\n L\u1eddi gi\u1ea3i:<\/b><\/p>\n <\/p>\n B\u00e0i 4 (trang 18 SGK H\u00ecnh h\u1ecdc 12):\u00a0Cho h\u00ecnh b\u00e1t di\u1ec7n \u0111\u1ec1u ABCDEF.<\/strong><\/span><\/p>\n Ch\u1ee9ng minh r\u1eb1ng:<\/strong><\/span><\/p>\n a)C\u00e1c \u0111o\u1ea1n th\u1eb3ng AF, BD v\u00e0 CE \u0111\u00f4i m\u1ed9t vu\u00f4ng g\u00f3c v\u1edbi nhau v\u00e0 c\u1eaft nhau t\u1ea1i trung \u0111i\u1ec3m m\u1ed7i \u0111\u01b0\u1eddng.<\/strong><\/span><\/p>\n b)ABFD, AEFC v\u00e0 BCDE l\u00e0 nh\u1eefng h\u00ecnh vu\u00f4ng.<\/strong><\/span><\/p>\n L\u1eddi gi\u1ea3i:<\/b><\/p>\n <\/p>\n a)Ta c\u00f3: B, C, D, E c\u00e1ch \u0111\u1ec1u A v\u00e0 F suy ra B, C, D, E c\u00f9ng n\u1eb1m tr\u00ean m\u1eb7t ph\u1eb3ng trung tr\u1ef1c c\u1ee7a \u0111o\u1ea1n th\u1eb3ng AF (1)<\/p>\n – Trong mp(BCDE), ta c\u00f3 BC = CD = DE = EB<\/p>\n Suy ra t\u1ee9 gi\u00e1c BCDE l\u00e0 h\u00ecnh thoi ho\u1eb7c h\u00ecnh vu\u00f4ng (2)<\/p>\n – M\u1eb7t kh\u00e1c AB = AC = AD = AE (3)<\/p>\n T\u1eeb (1), (2) v\u00e0 (3) suy ra BCDE l\u00e0 h\u00ecnh vu\u00f4ng.<\/p>\n V\u1eady BD v\u00e0 CE vu\u00f4ng g\u00f3c nhau v\u00e0 c\u1eaft nhau t\u1ea1i trung \u0111i\u1ec3m m\u1ed7i \u0111\u01b0\u1eddng.<\/p>\n Ch\u1ee9ng minh nh\u01b0 tr\u00ean ta suy ra AF v\u00e0 BD, AF v\u00e0 CE vu\u00f4ng g\u00f3c nhau v\u00e0 c\u1eaft nhau t\u1ea1i trung \u0111i\u1ec3m m\u1ed7i \u0111\u01b0\u1eddng.<\/p>\n b)Ta c\u00f3: BCDE l\u00e0 h\u00ecnh vu\u00f4ng (ch\u1ee9ng minh tr\u00ean).<\/p>\n T\u01b0\u01a1ng t\u1ef1, ABFD v\u00e0 AEFC c\u0169ng l\u00e0 nh\u1eefng h\u00ecnh vu\u00f4ng.<\/p>\n<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":" B\u00e0i 1 (trang 18 SGK H\u00ecnh h\u1ecdc 12):\u00a0C\u1eaft b\u00eca theo m\u1eabu d\u01b0\u1edbi \u0111\u00e2y (h.123), g\u1ea5p theo \u0111\u01b0\u1eddng k\u1ebb, r\u1ed3i d\u00e1n c\u00e1c m\u00e9p l\u1ea1i \u0111\u1ec3 \u0111\u01b0\u1ee3c c\u00e1c h\u00ecnh t\u1ee9 di\u1ec7n \u0111\u1ec1u, h\u00ecnh l\u1eadp ph\u01b0\u01a1ng v\u00e0 h\u00ecnh b\u00e1t di\u1ec7n \u0111\u1ec1u. L\u1eddi gi\u1ea3i: C\u00e1c b\u1ea1n h\u1ecdc sinh t\u1ef1 th\u1ef1c hi\u1ec7n. B\u00e0i 2 (trang 18 SGK H\u00ecnh h\u1ecdc 12):\u00a0Cho […]<\/p>\n","protected":false},"author":3,"featured_media":20737,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_mi_skip_tracking":false,"tdm_status":"","tdm_grid_status":""},"categories":[1298],"tags":[1377,1356,1355],"yoast_head":"\n