【简答题】凸透镜能使平行于主光轴的光线会聚于一点,这一点叫做凸透镜的______,这一点到凸透镜光心的距离叫做______.
【简答题】如图,在8×8的网格中,每个小正方形的顶点叫做格点,△OAB的顶点都在格点上,请你在网格中画出一个△OCD,使它的顶点在格点上,且使△OCD与△OAB相似,相似比为2︰1.
【简答题】在正方形网格内,小格的顶点叫做格点.以点D、E为两个顶点,作出所有位置不同的格点三角形,使所作的格点三角形与△ABC全等.
【简答题】力 F 使物体绕 O 点的转动效应用力矩来度量, F 与 d 的乘积加上正负号叫做力 F 对 O 点的矩,简称力矩。 O 点叫做 。 O 点到力 F 作用线的垂直距离 d 叫做 。
【单选题】In what type of test is the variable of interest the difference between the values of the observations rather than the observations themselves?
A.
a test for the equality of variances from 2 independent populations
B.
a test for the difference between the means of 2 related populations
C.
a test for the difference between the means of 2 independent populations
【单选题】In what type of test is the variable of interest the difference between the values of the observations rather than the observations themselves?
A.
A test for the equality of variances from two independent populations.
B.
A test for the mean difference between two related populations.
C.
A test for the difference between the means of two independent populations.
D.
all the options are correct .