I never wanted a dog, but now I'm so glad I have one.
About two years ago my wife, Cathy, got a little dog with a face only a mother could love. We named her Gertie. Gertie is the kind of dog that has to grow on you. So I decided that the dog would be trained. This didn't quite go as planned. At 15 weeks old, she was nearly made to leave the Pet smart Training School. She spent every night lying in our bed — snoring(打鼾) so loudly that I hardly got a good night's sleep.
Then, about six months after she arrived, I felt that something in my heart was taking place, and I was unable to stop it. My behavior began to change. I began to smile at people when passing them in a street. I started calling my kids and, to my surprise, they started calling me. I even tried to speak to my grandchildren over the phone once. I was even glad to listen to laughter from a 10-month-old granddaughter. The point is that I was changing.
My wife and I both agree that it is Gertie who has changed my behavior.
Gertie is now nearly two years old and almost fully grown. I have come to like the pet little by little, though she is my wife's dog.
阿基米德与“
定理”
阿基米德是古希腊的数学家、力学家,约公元前287年生于西西里岛的叙拉古,约公元前212年卒于叙拉古.阿基米德死后,他的墓碑上刻了一个等边圆柱,等边圆柱内部有一个内切球[如前面练习中第0104题的图(二).阿基米德的墓碑上为什么会刻上这一图形呢?原来这个图形所蕴涵的秘密,是阿基米德最为得意的发现.这个秘密是什么呢?想必同学们经过前面的计算已经发现了,那就是:如果等边圆柱中有一个内切球,则内切球的表面积是圆柱表面积的
,内切球的体积也是圆柱体积的
.这个数学结论的奇妙绝伦的确让人叹服,大自然的和谐完美令人惊奇.
通过这个例子,你体会到数学的神奇魅力了吗?
(
约为
,单位:
之比的常用对数称作声强的声强级,记作L(贝尔),即
,取贝尔的10倍作为响度的常用单位,简称为分贝,已知某处“喊
泉”的声音响度y(分贝)与喷出的泉水高度x(米)满足关系式
,现知A同学大喝一声激起的涌泉最高高度为50米,若A同学大喝一声的声强大约相当于10个B同学同时大喝一声的声强,则B同学大喝一声激起的涌泉最高高度约为米