设函数f(x)=2lnx．则f”(x)=

A <img src="https://www.beizhujiaoyu.com/uploads/202208/162089050434261.png" width="78" height="32" />  B <img src="https://www.beizhujiaoyu.com/uploads/202208/16208905087291.png" width="60" height="31" />  C <img src="https://www.beizhujiaoyu.com/uploads/202208/162089051341251.png" width="78" height="31" />  D <img src="https://www.beizhujiaoyu.com/uploads/202208/162089051871841.png" width="60" height="32" /> 

A 4 B 0 C 2 D -4

A 5x⁴ B <img src="https://www.beizhujiaoyu.com/uploads/202208/162089054536771.png" width="19" height="52" />x⁴ C 1+x⁴ D x⁴

A 2y B 2xy C 3x²+y² D 3x²+2xy

A (1+cosx)dx B (1+2cosx)dx C (1-cosx)dx D (1-2cosx)dx

A xdx-4ydy B xdx-ydy C 2xdx-4ydy D 2xdx-8ydy

A 圆锥面 B 球面 C 旋转抛物面 D 柱面

A 2 B 1 C <img src="https://www.beizhujiaoyu.com/uploads/202208/16208905642721.png" width="20" height="52" /> D <img src="https://www.beizhujiaoyu.com/uploads/202208/162089056968471.png" width="20" height="52" />

A Cre^x B Cxe^-x C Ce^x D Ce^-x