hộ mk câu b với câu c với đang cần gấp

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hộ mk câu b với câu c với
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9 months 2021-04-29T00:51:06+00:00 1 Answers 4 views 0

$$\begin{array}{l} b)Vi – et:\left\{ \begin{array}{l} {x_1} + {x_2} = – m\\ {x_1}{x_2} = m + m = 2m \end{array} \right.\\ {x_1}^2 + {x_2}^2 = {x_1}^2 + {x_2}^2 + 2{x_1}{x_2} – 2{x_1}{x_2}\\ = {\left( {{x_1} + {x_2}} \right)^2} – 2{x_1}{x_2}\\ = {m^2} – 2.2m = {m^2} – 4m\\ {x_1}^3 + {x_2}^3 = \left( {{x_1} + {x_2}} \right)\left( {{x_1}^2 – {x_1}{x_2} + {x_2}^2} \right)\\ = \left( {{x_1} + {x_2}} \right)\left[ {{x_1}^2 + 2{x_1}{x_2} + {x_2}^2 – 3{x_1}{x_2}} \right]\\ = \left( {{x_1} + {x_2}} \right)\left[ {{{\left( {{x_1} + {x_2}} \right)}^2} – 3{x_1}{x_2}} \right]\\ = – m\left( {{m^2} – 3.2m} \right)\\ = – m\left( {{m^2} – 6m} \right)\\ = – {m^3} + 6{m^2}\\ c)Xét:\Delta \ge 0\\ \to {m^2} – 4.m.m \ge 0\\ \to {m^2} – 4{m^2} \ge 0\\ \to – 3{m^2} \ge 0\\ \to {m^2} \le 0\\ \to m = 0\\ Xét:{x_1}^2 + {x_2}^2 = 9\\ \to {x_1}^2 + {x_2}^2 + 2{x_1}{x_2} – 2{x_1}{x_2} = 9\\ \to {\left( {{x_1} + {x_2}} \right)^2} – 2{x_1}{x_2} = 9\\ \to {m^2} – 2.2m = 9\\ \to {m^2} – 4m = 9\left( {vô nghiệm} \right) \end{array}$$