【多选题】我国及 IEC (国际电工委员会)都对安全电压的上限值进行了规定,即工频下安全电压的上限值为( ) V ,其电压等级有 42V 、 36V 、( ) V 、12 V 、( ) V 。同时规定:高度不足 2.5M 的照明装置、机床局部照明灯具、移动行灯等,其安全电压可采用( ) V 为安全电压。
【简答题】在△ABC中,已知a+b=12,∠A=60°,∠B=45°,求a,b。
【单选题】已知,在△ ABC 中,∠ A=60° ,∠ C=80° ,则∠ B= ( )
【简答题】由下列条件解题:在Rt△ABC中,∠C=90°: (1)已知a=4,b=8,求c. (2)已知b=10,∠B=60°,求a,c. (3)已知c=20,∠A=60°,求a,b.
【简答题】在Rt△ABC中,∠C=90°,已知AB= 3 ,∠A=60°,则BC=______.
【单选题】教育者指导幼儿就某些社会性问题、现象、事物相互启发、交流意见的方法,被称为
【单选题】Price discrimination by a monopolist is less effective if the
B.
good has no substitutes.
C.
monopolist can identify buyers by willingness to pay.
D.
good cannot be resold.
【单选题】A major difference between a single-price monopolist and a perfectly competitive firm is that the
A.
monopolist can maximize profit by setting the price of the output where demand is inelastic.
B.
monopolist can always increase its profits by increasing the price of its output.
C.
monopolist's marginal revenue is less than price.
D.
monopolist is guaranteed to earn an economic profit.