Cho hình hộp chữ nhật ABCD.A'B'C;D' có \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyqaiaadk % eacqGH9aqpcaWGHbGaaiilaiaadgeacaWGebGaeyypa0JaaGOmaiaa % dggacaGGSaGaamyqaiaadoeacaGGNaGaeyypa0ZaaOaaaeaacaaI2a % aaleqaaOGaamyyaaaa!440E! AB = a,AD = 2a,AC' = \sqrt 6 a\) Thể tích khối hộp chữ nhật ABCD.A'B'C'D' bằng:
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Lời giải:
Báo saiTa có: \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyqaiaado % eacqGH9aqpdaGcaaqaaiaadgeacaWGcbWaaWbaaSqabeaacaaIYaaa % aOGaey4kaSIaamOqaiaadoeadaahaaWcbeqaaiaaikdaaaaabeaaki % abg2da9maakaaabaGaamyyamaaCaaaleqabaGaaGOmaaaakiabgUca % RiaaisdacaWGHbWaaWbaaSqabeaacaaIYaaaaaqabaGccqGH9aqpca % WGHbWaaOaaaeaacaaI1aaaleqaaaaa!47AA! AC = \sqrt {A{B^2} + B{C^2}} = \sqrt {{a^2} + 4{a^2}} = a\sqrt 5 \) (định lý Pitago)
Xét tam giác ACC’ vuông tại C ta có:
\(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGceaqabeaacaWGdb % Gaam4qaiaacEcacqGH9aqpdaGcaaqaaiaadgeacaWGdbGaai4jamaa % CaaaleqabaGaaGOmaaaakiabgkHiTiaadgeacaWGdbWaaWbaaSqabe % aacaaIYaaaaaqabaGccqGH9aqpdaGcaaqaaiaaiAdacaWGHbWaaWba % aSqabeaacaaIYaaaaOGaeyOeI0IaaGynaiaadggadaahaaWcbeqaai % aaikdaaaaabeaakiabg2da9iaadggaaeaacqGHshI3caWGwbWaaSba % aSqaaiaadgeacaWGcbGaam4qaiaadseacaGGUaGaamyqaiaacEcaca % WGcbGaai4jaiaadoeacaGGNaGaamiraiaacEcaaeqaaOGaeyypa0Ja % am4qaiaadoeacaGGNaGaaiOlaiaadgeacaWGcbGaaiOlaiaadgeaca % WGebGaeyypa0Jaamyyaiaac6cacaWGHbGaaiOlaiaaikdacaWGHbGa % eyypa0JaaGOmaiaadggadaahaaWcbeqaaiaaiodaaaaaaaa!6739! \begin{array}{l} CC' = \sqrt {AC{'^2} - A{C^2}} = \sqrt {6{a^2} - 5{a^2}} = a\\ \Rightarrow {V_{ABCD.A'B'C'D'}} = CC'.AB.AD = a.a.2a = 2{a^3} \end{array}\)
Đề thi thử tốt nghiệp THPT QG môn Toán năm 2020
Tuyển chọn số 4