Cho số phức z thỏa mãn \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOEaiabgU % caRiaaikdadaqdaaqaaiaadQhaaaGaeyypa0JaaGOnaiabgUcaRiaa % ikdacaWGPbaaaa!3DF3! z + 2\overline z = 6 + 2i\). Điểm biểu diễn số phức z có tọa độ là:
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Lời giải:
Báo saiGọi số phức \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOEaiabg2 % da9iaadggacqGHRaWkcaWGIbGaamyAaiaacYcadaqadaqaaiaadgga % caGGSaGaamOyaiabgIGiolabl2riHcGaayjkaiaawMcaaaaa!4340! z = a + bi,(a,b \in R)\). Khi đó ta có:\(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaaca % WG6baaaiabg2da9iaadggacqGHsislcaWGIbGaamyAaaaa!3BB2! \overline z = a - bi\)
Khi đó ta có : \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGceaqabeaacaWG6b % Gaey4kaSIaaGOmamaanaaabaGaamOEaaaacqGH9aqpcaaI2aGaey4k % aSIaaGOmaiaadMgacqGHuhY2caWGHbGaey4kaSIaamOyaiaadMgacq % GHRaWkcaaIYaWaaeWaaeaacaWGHbGaeyOeI0IaamOyaiaadMgaaiaa % wIcacaGLPaaacqGH9aqpcaaI2aGaey4kaSIaaGOmaiaadMgaaeaacq % GHuhY2caaIZaGaamyyaiabgkHiTiaadkgacaWGPbGaeyypa0JaaGOn % aiabgUcaRiaaikdacaWGPbGaeyi1HS9aaiqaaqaabeqaaiaaiodaca % WGHbGaeyypa0JaaGOnaaqaaiabgkHiTiaadkgacqGH9aqpcaaIYaaa % aiaawUhaaiabgsDiBpaaceaaeaqabeaacaWGHbGaeyypa0JaaGOmaa % qaaiaadkgacqGH9aqpcqGHsislcaaIYaaaaiaawUhaaiabgkDiElaa % dQhacqGH9aqpcaaIYaGaeyOeI0IaaGOmaiaadMgaaaaa!7613! \begin{array}{l} z + 2\overline z = 6 + 2i \Leftrightarrow a + bi + 2\left( {a - bi} \right) = 6 + 2i\\ \Leftrightarrow 3a - bi = 6 + 2i \Leftrightarrow \left\{ \begin{array}{l} 3a = 6\\ - b = 2 \end{array} \right. \Leftrightarrow \left\{ \begin{array}{l} a = 2\\ b = - 2 \end{array} \right. \Rightarrow z = 2 - 2i \end{array}\)
\(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeyO0H4Taam % ytamaabmaabaGaaGOmaiaacUdacqGHsislcaaIYaaacaGLOaGaayzk % aaaaaa!3DD0! \Rightarrow M\left( {2; - 2} \right)\) là điểm biểu diễn số phức z.
Đề thi thử tốt nghiệp THPT QG môn Toán năm 2020
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