平面直角坐标系xOy中，点A、B分别在函数y₁= $\frac{4}{x}$ （x＞0）与y₂=﹣ $\frac{4}{x}$ （x＜0）的图象上，A、B的横坐标分别为

a、b．

（2015•天水）如图1所示，电源电压U=12V，R₁为定值电阻，阻值为24Ω，R₂为滑动变阻器，R₂的最大阻值为48Ω，小灯泡标有“6V  3W”字样，小灯泡的U﹣I关系如图2所示．求：

【解答】解：（1）灯泡正常工作时，两端的电压为U_L=6V，由P=UI可得，

灯泡正常工作时通过灯丝的电流I_L=$\frac{P}{U_L}$=$\frac{3}{6}$=0.5A；

（2）当S闭合，S₁、S₂都断开时，等效电路图如下图所示：

当小灯泡两端的电压为4V时，由图象可知电路中的电流I=0.4A，

滑动变阻器接入电阻的阻值R_滑=$\frac{U-U_L\text{'}}{I}$=$\frac{12-4}{0.4}$=20Ω；

答：（1）小灯泡正常工作时通过灯丝的电流是0.5A；

（2）滑动变阻器接入电路中的电阻值为20Ω．

    Britain's smallest school was closed down because its only pupil failed to turn up for class, a famous Britain newspaper reported in May.
The newspaper said the six-year-old girl's parents were unhappy with a teacher who just got the new job to teach the only pupil.
The school had been closed for the last nine months after its former（前任的）teacher retired and the only other pupil moved on to a secondary（中等的）school. The new teacher, Ms. Puckey was to start teaching the girl and reopen（再次打开）the school.
But the girl's mother is keeping her daughter at home.
    “I was not pleased with the new teacher,”the mother said. “I had told the old teacher as far back as last September that if Ms. Puckey got the job, my child would not be going to school.”
    The school lies on an island off the northeast of Scotland. Although there was only one pupil, the school is very good in many ways and has a headmaster, three computers, a television, and an art room as well as a school house with three bedrooms.