Gọi (H) là đồ thị hàm số \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyEaiabg2 % da9maalaaabaGaaGOmaiaadIhacqGHRaWkcaaIZaaabaGaamiEaiab % gUcaRiaaigdaaaaaaa!3DF9! y = \frac{{2x + 3}}{{x + 1}}\). Điểm \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamytaiaacI % cacaWG4bWaaSbaaSqaaiaaicdaaeqaaOGaai4oaiaadMhadaWgaaWc % baGaaGimaaqabaGccaGGPaaaaa!3CB9! M({x_0};{y_0})\) thuộc (H) có tổng khoảng cách đến hai đường tiệm cận là nhỏ nhất, với \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamiEamaaBa % aaleaacaaIWaaabeaakiabgYda8iaaicdaaaa!399F! {x_0} < 0\) khi đó \(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamiEamaaBa % aaleaacaaIWaaabeaakiabgUcaRiaadMhadaWgaaWcbaGaaGimaaqa % baaaaa!3AA7! {x_0} + {y_0}\) bằng?
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Lời giải:
Báo saiTập xác định.R\{1}
Dễ có tiệm cận đứng \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamizamaaBa % aaleaacaaIXaaabeaakiaacQdacaaMe8UaamiEaiabg2da9iabgkHi % Tiaaigdaaaa!3DC3! {d_1}:\;x = - 1\) và tiệm cận ngang \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamizamaaBa % aaleaacaaIYaaabeaakiaacQdacaWG5bGaeyypa0JaaGOmaaaa!3B4C! {d_2}:y = 2\).
Ta có \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamizamaabm % aabaGaamytaiaacYcacaaMe8UaamizamaaBaaaleaacaaIXaaabeaa % aOGaayjkaiaawMcaaiaaysW7cqGHRaWkcaWGKbWaaeWaaeaacaWGnb % GaaiilaiaaysW7caWGKbWaaSbaaSqaaiaaikdaaeqaaaGccaGLOaGa % ayzkaaGaeyypa0ZaaqWaaeaacaWG4bWaaSbaaSqaaiaaicdaaeqaaO % Gaey4kaSIaaGymaaGaay5bSlaawIa7aiabgUcaRmaaemaabaWaaSaa % aeaacaaIYaGaamiEamaaBaaaleaacaaIWaaabeaakiabgUcaRiaaio % daaeaacaWG4bWaaSbaaSqaaiaaicdaaeqaaOGaey4kaSIaaGymaaaa % cqGHsislcaaIXaaacaGLhWUaayjcSdaaaa!5C59! d\left( {M,\;{d_1}} \right)\; + d\left( {M,\;{d_2}} \right) = \left| {{x_0} + 1} \right| + \left| {\frac{{2{x_0} + 3}}{{{x_0} + 1}} - 1} \right|\)\(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeyypa0Zaaq % WaaeaacaWG4bWaaSbaaSqaaiaaicdaaeqaaOGaey4kaSIaaGymaaGa % ay5bSlaawIa7aiabgUcaRmaaemaabaWaaSaaaeaacaaIXaaabaGaam % iEamaaBaaaleaacaaIWaaabeaakiabgUcaRiaaigdaaaaacaGLhWUa % ayjcSdGaeyyzImRaaGOmaaaa!4880! = \left| {{x_0} + 1} \right| + \left| {\frac{1}{{{x_0} + 1}}} \right| \ge 2\)
Đẳng thức xảy ra khi và chỉ khi \(% MathType!MTEF!2!1!+- % feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaqWaaeaaca % WG4bWaaSbaaSqaaiaaicdaaeqaaOGaey4kaSIaaGymaaGaay5bSlaa % wIa7aiabg2da9maaemaabaWaaSaaaeaacaaIXaaabaGaamiEamaaBa % aaleaacaaIWaaabeaakiabgUcaRiaaigdaaaaacaGLhWUaayjcSdGa % eyi1HSTaamiEamaaBaaaleaacaaIWaaabeaakiabg2da9iaaicdacq % GHOiI2caWG4bWaaSbaaSqaaiaaicdaaeqaaOGaeyypa0JaeyOeI0Ia % aGOmaaaa!5171! \left| {{x_0} + 1} \right| = \left| {\frac{1}{{{x_0} + 1}}} \right| \Leftrightarrow {x_0} = 0 \vee {x_0} = - 2\). Vì \(x_0 < 0\) nên \(x_0 = -2\)\(% MathType!MTEF!2!1!+- % feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeyO0H4Taam % yEamaaBaaaleaacaaIWaaabeaakiabg2da9iaaigdacqGHshI3caWG % 4bWaaSbaaSqaaiaaicdaaeqaaOGaey4kaSIaamyEamaaBaaaleaaca % aIWaaabeaakiabg2da9iabgkHiTiaaigdaaaa!45C8! \Rightarrow {y_0} = 1 \Rightarrow {x_0} + {y_0} = - 1\)