Trong các số phức z thỏa mãn \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaqWaaeaada % WcaaqaamaabmaabaGaaGymaiaaikdacqGHsislcaaI1aGaamyAaaGa % ayjkaiaawMcaaiaadQhacqGHRaWkcaaIXaGaaG4naiabgUcaRiaaiE % dacaWGPbaabaGaamOEaiabgkHiTiaaikdacqGHsislcaWGPbaaaaGa % ay5bSlaawIa7aiabg2da9iaaigdacaaIZaaaaa!4BAE! \left| {\frac{{\left( {12 - 5i} \right)z + 17 + 7i}}{{z - 2 - i}}} \right| = 13\). Tìm giá trị nhỏ nhất của |z|.
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Lời giải:
Báo sai\(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaqWaaeaada % WcaaqaamaabmaabaGaaGymaiaaikdacqGHsislcaaI1aGaamyAaaGa % ayjkaiaawMcaaiaadQhacqGHRaWkcaaIXaGaaG4naiabgUcaRiaaiE % dacaWGPbaabaGaamOEaiabgkHiTiaaikdacqGHsislcaWGPbaaaaGa % ay5bSlaawIa7aiabg2da9iaaigdacaaIZaGaeyO0H49aaqWaaeaada % qadaqaaiaaigdacaaIYaGaeyOeI0IaaGynaiaadMgaaiaawIcacaGL % PaaacaWG6bGaey4kaSIaaGymaiaaiEdacqGHRaWkcaaI3aGaamyAaa % Gaay5bSlaawIa7aiabg2da9iaaigdacaaIZaWaaqWaaeaacaWG6bGa % eyOeI0IaaGOmaiabgkHiTiaadMgaaiaawEa7caGLiWoaaaa!66D8! \left| {\frac{{\left( {12 - 5i} \right)z + 17 + 7i}}{{z - 2 - i}}} \right| = 13 \Rightarrow \left| {\left( {12 - 5i} \right)z + 17 + 7i} \right| = 13\left| {z - 2 - i} \right|\)
\(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeyi1HS9aaq % WaaeaacaaIXaGaaGOmaiabgkHiTiaaiwdacaWGPbaacaGLhWUaayjc % SdWaaqWaaeaacaWG6bGaey4kaSYaaSaaaeaacaaIXaGaaG4naiabgU % caRiaaiEdacaWGPbaabaGaaGymaiaaikdacqGHsislcaaI1aGaamyA % aaaaaiaawEa7caGLiWoacqGH9aqpcaaIXaGaaG4mamaaemaabaGaam % OEaiabgkHiTiaaikdacqGHsislcaWGPbaacaGLhWUaayjcSdGaeyi1 % HS9aaqWaaeaacaWG6bGaey4kaSIaaGymaiabgUcaRiaadMgaaiaawE % a7caGLiWoacqGH9aqpdaabdaqaaiaadQhacqGHsislcaaIYaGaeyOe % I0IaamyAaaGaay5bSlaawIa7aaaa!696B! \Leftrightarrow \left| {12 - 5i} \right|\left| {z + \frac{{17 + 7i}}{{12 - 5i}}} \right| = 13\left| {z - 2 - i} \right| \Leftrightarrow \left| {z + 1 + i} \right| = \left| {z - 2 - i} \right|\)
Đặt \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOEaiabg2 % da9iaadIhacqGHRaWkcaWG5bGaamyAaiaacYcadaWadaqaamaabmaa % baGaamiEaiaacUdacaWG5baacaGLOaGaayzkaaGaeyiyIK7aaeWaae % aacaaIYaGaai4oaiaaigdaaiaawIcacaGLPaaaaiaawUfacaGLDbaa % aaa!482E! z = x + yi,\left[ {\left( {x;y} \right) \ne \left( {2;1} \right)} \right]\) ta có \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaeWaaeaaca % WG4bGaey4kaSIaaGymaaGaayjkaiaawMcaamaaCaaaleqabaGaaGOm % aaaakiabgUcaRmaabmaabaGaamyEaiabgUcaRiaaigdaaiaawIcaca % GLPaaadaahaaWcbeqaaiaaikdaaaGccqGH9aqpdaqadaqaaiaadIha % cqGHsislcaaIYaaacaGLOaGaayzkaaWaaWbaaSqabeaacaaIYaaaaO % Gaey4kaSYaaeWaaeaacaWG5bGaeyOeI0IaaGymaaGaayjkaiaawMca % amaaCaaaleqabaGaaGOmaaaakiabgsDiBlaaiAdacaWG4bGaey4kaS % IaaGinaiaadMhacqGHsislcaaIZaGaeyypa0JaaGimaiaaykW7caaM % c8+aaeWaaeaacaWGKbaacaGLOaGaayzkaaaaaa!5CD7! {\left( {x + 1} \right)^2} + {\left( {y + 1} \right)^2} = {\left( {x - 2} \right)^2} + {\left( {y - 1} \right)^2} \Leftrightarrow 6x + 4y - 3 = 0\,\,\left( d \right)\)
Vậy tập hợp điểm biểu diễn số phức z là đường thẳng \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamizaiaacQ % dacaaI2aGaamiEaiabgUcaRiaaisdacaWG5bGaeyOeI0IaaG4maiab % g2da9iaaicdacaaMc8oaaa!40EA! d:6x + 4y - 3 = 0\)
\(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaqWaaeaaca % WG6baacaGLhWUaayjcSdWaaSbaaSqaaiGac2gacaGGPbGaaiOBaaqa % baGccqGH9aqpcaWGpbGaamytamaaBaaaleaaciGGTbGaaiyAaiaac6 % gaaeqaaOGaeyypa0JaamizamaabmaabaGaam4taiaacUdacaWGKbaa % caGLOaGaayzkaaGaeyypa0ZaaSaaaeaacaaIYaWaaOaaaeaacaaIXa % GaaG4maaWcbeaaaOqaaiaaikdacaaI2aaaaaaa!4DAF! {\left| z \right|_{\min }} = O{M_{\min }} = d\left( {O;d} \right) = \frac{{2\sqrt {13} }}{{26}}\)
Đề thi thử tốt nghiệp THPT QG môn Toán năm 2020
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