看到数学组很冷清,就贴这里。给儿子出了一道数学题,我们觉得我的答案是对的,但是不知道他的答案为什么不对。题目是这样的(自己编的,英文不利索):
A machine is formed with two sticks with same length of 1. One end of the stick OA is fixed at O and can spin around. The other stick AB connect OA at A with a joint. AB is very heavy so when OA spins, it’s always straight down. What would the area the machine swept out when OA finishes a circle?
我的答案是: pi + 2, 因为上下凑成一元,中间是一个2x1的长方形,
他的答案是:2pi, 因上面一个元,面积是pi,下面是由上下半圆长,等距1的弧形,面积也是 pi,总共是2pi