【简答题】在平面直角坐标系xOy中,一次函数y=- x+3的图象与x轴交于点A,与y轴交于点B,动点P从点B出发沿BA向终点A运动,同时动点Q从点O出发沿OB向点B运动,到达点B后立刻以原来的速度沿BO返回.点P,Q运动速度均为每秒1个单位长度,当点P到达点A时停止运动,点Q也同时停止.连结PQ,设运动时间为t(t>0)秒. (1)求点P的坐标(用含t的代数式表示); (2)当点Q从点O向点B运动时(未到达...
【单选题】The difference between a permutation and a combination is
A.
a combination is based on the classical definition of probability.
B.
in a permutation order is not important and in a combination it is important.
C.
in a permutation order is important and in a combination order is not important.
D.
a permutation is based on the classical definition of probability.
【判断题】电枢反应对并励电动机转速特性和转矩特性有一定的影响,当电枢电流 Ia 增加时,转速 n 将下降 ,转矩 Te 将增加 。
【单选题】Injectors on modern engines are cooled by a combination of the intensive bore cooling in the cylinder by a combination of the intensive bore pockets and by the fuel which is re-circulated through the ...
【简答题】2) 电枢反应对并励电动机转速特性和转矩特性有一定的影响,当电枢电流 增加时,转速 n 将 ,转矩 T M 将 。
【单选题】晶体管共发射极放大电路具有( )的作用。
【简答题】从化学结构上看,糖类是()或(),或者()后可以生成多羟基醛或多羟基酮的化合物。