[tex=18.286x1.286]7OzYu1fkCTQhBaQ8JK5MihLO8K7JOq0YgI4KuD2N0qOuDdkVckXvxyX4wZA+7kXVRyFGhGuv74eICwzfXriK7g==[/tex]

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下列选项为某变速器一、二、三、四挡的传动比，则三挡的传动比为（）。 A: 0.969 B: 1.286 C: 1.944 D: 3.455

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假定在连续[tex=1.0x1.286]oqTX8Aml1lQZAP0gMGUYCw==[/tex]个周末所观察的股票价格（以美元计)为:[tex=15.571x1.286]qiPxfL6zZuIVuHcgqAoTEJIo3Qp7yqYtiL0vrGnJ34S7ANs953NEvKX6X2vdVfJk[/tex][tex=18.286x1.286]Sn9V8mVoGUcUMFsFr2BHs9uEZ4QFUaRgcACdW96mMVc1M9zgsIGlk0a36oAB6/gPlicGpYN1vDwycjm9RR2t0g==[/tex][tex=4.429x1.286]GfqMcJaRZgxKIEtQFkWbWcBd7cPgCfUEGWvGXwhcORM=[/tex]估计股票价格的波动率，你所估计结果的标准差为多少?

下列变量组（）是一个闭回路。 A: {x，x，x，x，x，x} B: {x，x，x，x，x} C: {x，x，x，x，x，x} D: {x，x，x，x，x，x}

以下谓词蕴含式正确的是（）: (∀x) (A(x)→B(x))=>( ∀x)A(x)→(∀x)B(x)|(∀x) (A(x)↔B(x))=>( ∀x)A(x)↔(∀x)B(x)|(∀x)A(x)∨(∀x)B(x)=>( ∀x) (A(x)∨B(x))|(∃x) (A(x)∧B(x))=>(∃x)A(x)∧(∃x)B(x)

以下谓词蕴含式正确的是（）: (?x) (A(x)→B(x))=>( ?x)A(x)→(?x)B(x)|(?x) (A(x)?B(x))=>( ?x)A(x)?(?x)B(x)|(?x)A(x)∨(?x)B(x)=>( ?x) (A(x)∨B(x))|(?x) (A(x)∧B(x))=>(?x)A(x)∧(?x)B(x)

下列式中错误的是： A: (∀x)(A(x)Úp(x)) Û (∀x)A(x)Ú (∀x)p(x) B: ($x)A(x) Ù p Û ($x)(A(x) Ù p ) C: (∀x)(A(x)ÚB(x)) Þ (∀x)A(x)Ú( ∀x)B(x) D: ($x)(A(x)ÙB(x)) Þ ($x)A(x)Ù( $x)B(x)

判断下列推证是否正确。 (∀x)(A(x)→B(x))⇔(∀x)(￢A(x)∨B(x)) ⇔(∀x)￢( A(x)∧￢B(x) ) ⇔￢(∃x) ( A(x)∧￢B(x) ) ⇔￢( (∃x)A(x)∧(∃x)￢B(x) ) ⇔￢(∃x)A(x)∨￢(∃x)￢B(x) ⇔￢(∃x)A(x)∨(∀x)B(x) ⇔(∃x)A(x)→(∀x)B(x)