简答题:用薄铁皮做成一个容积为V₀的有盖长方匣，其底为正方形，由于下底面无须喷漆，故其每单位面积成本仅为其余各面的一半，问长方匣的底面长为多少时，才能使匣子的造价最低?

A x²+2 B <img width="75" height="51" src="https://www.beizhujiaoyu.com/uploads/202208/20220309101223_1814.jpg" /> C x² D x²-2

A 8 B 7 C 9 D 6

A 1 B -1 C 0 D 2

A -e^-sin(xy) B -sin(xy)e^-sin(xy) C -xcos(xy)e^-sin(xy) D -e^-cos(xy)

A <img width="142" height="42" src="https://www.beizhujiaoyu.com/uploads/202208/20220309101239_9456.jpg" /> B <img width="113" height="52" src="https://www.beizhujiaoyu.com/uploads/202208/20220309101241_1644.jpg" /> C <img width="112" height="42" src="https://www.beizhujiaoyu.com/uploads/202208/20220309101242_1488.jpg" /> D <img width="142" height="51" src="https://www.beizhujiaoyu.com/uploads/202208/20220309101243_3675.jpg" />

A 不一定可微 B 可微 C 极限不一定存在 D 不一定连续

A x=-1 B x=1 C y=0 D y=1

A 0 B π C <img width="25" height="42" src="https://www.beizhujiaoyu.com/uploads/202208/20220309101259_1798.jpg" /> D <img width="74" height="42" src="https://www.beizhujiaoyu.com/uploads/202208/20220309101300_0727.jpg" />

A 0 B 1 C 2 D 不存在

A 6π B 3π C 30π D 4 π