Then CF⊥BD and cf ⊥ d1d.

∴cf⊥b 1e∴cf⊥ airplane BB 1D 1D

(II)∵CF⊥ plane BDD 1B 1,

∴CF⊥ plane EFB 1, cf = BF = 2,

∫ef = 12bd 1 = 3, b1f = bf2+bb12 = (2) 2+22 = 6, b1e = b/kloc-. Other similar problems 2022-11-13 are shown in the figure, in the cube ABCD-a1b1c65438+DD1with length 2. 2022-08- 12 In the cube ABCD-A1b1c1,e and f are the midpoint of DD 1 and DB, respectively. Verification: EF is perpendicular to B 1C65438+. In the cube ABCD-A1B1C1D1,E and F are DD 1, and the midpoint of DB is142012-/Kloc. E and f are DD 1 respectively, and the midpoint of DB is 2420 10- 10-07. As shown in the figure, in the cube ABCD-A1B1C1D1with side length A, e and f are dd65438 respectively. The midpoint of bb132011-06-04 is in the cube ABCD-a1b1c1d1,where e and f are DD/respectively. Find (1) to prove EF// plane ABC1d1602020-03-02. In the cube ABCD-a1b1c1d1,e and f are DD 65438 respectively. Verification: EF vertical B1C2020-01-kloc-0/8 is shown in the figure, and the cube ABCD-A1b1c1d1is in the middle. The midpoint 5 of BB 1 is recommended to you: F.context('cmsRight', [{'URL':'/d01373f082025aaf51aa256e9edab64034f/kloc-0. x-BCE-process = image % 2f resize % 2Cm _ lfit % 2Cw _ 450% 2Ch _ 600% 2c limit _ 1% 2f quality % 2Cq _ 85% 2f format % 2Cf _ auto '，' contractId':'A24KA00562 '，}，{ ' URL ':/s？ word = % E6 % AC % A7 % E6 % B4 % B2 % E6 % 9D % AF & sa = searchpromo _ ozb _ zhidao _ tuijian '，' src ':'/3 BF 33 a 87 e 950352 AAF 5 df 4954 143 fbf2b 2 1 18 b6b？ x-BCE-process = image % 2f resize % 2Cm _ lfit % 2Cw _ 450% 2Ch _ 600% 2c limit _ 1% 2f quality % 2Cq _ 85% 2f format % 2Cf _ auto '，' contractId ':' '，}])； Is Huaqiang North's second-hand mobile phone reliable? Why is the cost of cancer treatment getting higher and higher? What impact will the "network toilet" have? The price of electric cars has dropped many times. Is the quality guaranteed? I recommend f.context ('recbrand', [{"img": "\/86D6277F9E2F07083523F69DFB 24B 899A901F20d? x-BCE-process = image % 2f resize % 2Cm _ lfit % 2Cw _ 450% 2Ch _ 600% 2c limit _ 1% 2f quality % 2Cq _ 85% 2f format % 2Cf _ auto "，" url":"/hm.js？ 6859 ce 5a af 00 FB 00387 e 6434 E4 FCC 925 "； var s = document . getelementsbytagname(" script ")[0]； s.parentNode.insertBefore(hm，s)； })(); window . TT = 172003597 1；