求 [tex=11.5x2.929]6HiiPBiQtKDs5hqgvIXpmPz3bqJ8TH1BVPDVpMOOfrJUyt6hIv4dkLWGxiaqVROr3ce7YvjOEdLFxmGmRuANyE4IAoRxSXItLBweWyPphLOeV2ROz/UCj7zaOHsXrdOXoepqFRRGjQ2cJLKtDZ2hBA==[/tex] 其中[tex=19.786x3.357]72YwY1v17IOM9Fxyttt1lwSAfdMVZb6GixiTExHJzAApiPZDsJD/o7UYj6Nt4mpWpA9csqCt4xwi+tVGfOb0KJWAr4Zu4siBs8FeCv5jgPUinl9UkaJaHlNhJrA2LFhnaeQ2m9YN9HQI4+Db+l2h7dFplIVAeI517HvpCfPs2dJtWhCrQ1fgp11hTX37ukxE[/tex]

假设函数[tex=12.357x1.571]uAEyfspjewsilX5675tTfdFHCb4a9YpiQASslGzK1tAFRcUDKXHRYD/cebOHj5zbFARovO1Kqr4uaGNKNnxUTybLhh0Xh7v/FG7yUwv9ERg7SbMnFnlqOzM+5cEpPYQf[/tex]，且存在非零常数A,B和b>0，使得[tex=18.429x2.214]u5Ei/jC+B48Hely8KmsjTKNOgqedFiZ4jWZaux4Qzxef2Be/WfPYlxGQGdHFAZEp0SbN7Bnbh1IpeNyvSHxXVTQVO6x5LY0F4JJO7nMDE8soiH3FXYcSdWsxYDjvgDjIAT6EQq0crpiu3zM7o8QO4g==[/tex]，证明一维波动方程初值问题[tex=19.786x3.357]fnpmC2J6JmQBLyo5NmGAzz1EEFvh0W+KMVB3PRTO6PCr+9Cu2nJO0+TLZ61SGNhKW9jKfd7HgXX0/9r3C4By6AWNgiiUyyT2F6C1M3jE5gSUUGTbal6F2v3yOrGogu2y3YxKbsrSRV70py367LhEWadddt7juSMStXLOxIDOWTj/VC6nY/avghHtwmCEDMYtLD0CbqraO2W1glBpBpcZgA==[/tex]的解u=u(x,t)满足：存在常数c，使得[tex=7.571x2.0]aQeshb8uwXT2rSAknc2RhUhDp0yVFK0kA0m5HWkd2GZeW72KX3pvv4u9jmoqFghq[/tex]，并且确定该常数c.

图示压杆体系中，弹簧支座刚度为[img=64x44]180379b3117202b.png[/img]，则该体系的临界荷载为kl的（ ）倍。[img=3924x1660]180379b32884d13.jpg[/img] A: 0.411 B: 1 C: 1.645 D: 3.357

图示压杆体系中，弹簧支座刚度为[img=64x44]1802df48734317e.png[/img]，则该体系的临界荷载为kl的（ ）倍。[img=3924x1660]1802df4888c0309.jpg[/img] A: 0.411 B: 1 C: 1.645 D: 3.357

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)

以下谓词公式中，( )不是逻辑有效式。 A: ($x)(P(x)∧Q(x)) Þ ($x) P(x)∧($x) Q(x) B: ("x)(P(x)∧Q(x)) Þ ("x) P(x)∧("x) Q(x) C: ($x)(P(x)∧Q(x)) Û ($x) P(x)∧($x) Q(x) D: ("x)(P(x)∧Q(x)) Û ("x) P(x)∧("x) Q(x)