我们家有一圆形的水缸,这天,我妈叫我测一下周长,想给水缸做个盖子。我想,周长公式是2πr,那就要测r,就要找圆心。于是,我找了两根木棒,交叉之后放在缸上面找圆心。我妈看了半天,问:“你在干啥?”“测半径算周长啊!”“你不能直接拿根毛线绕一圈吗?”……我忽然觉得这么多年书白读了。 Our family has a round water tank, this day, my mother asked me to measure the circumference, I would like to give the tank a lid. I think the perimeter formula is 2πr, it should be measured r, we must find the center of the circle. So, I found two sticks, after the cross on the cylinder to find the center of the circle. My mom looked for a long time and asked: “What are you doing? ” “Calculate the radius of the perimeter ah! ” “You can not take the root yarn around it?” "... I suddenly felt so many years White book read.