圆的曲率半径是圆半径吗?
来源:学生作业帮 编辑:搜搜考试网作业帮 分类:数学作业 时间:2024/07/16 15:58:30
圆的曲率半径是圆半径吗?
如果是?根据这个R=(1+y'^2)^(3/2)/y" 公式怎么推出来曲率半径是圆半径?
如果是?根据这个R=(1+y'^2)^(3/2)/y" 公式怎么推出来曲率半径是圆半径?
![圆的曲率半径是圆半径吗?](/uploads/image/z/3098557-37-7.jpg?t=%E5%9C%86%E7%9A%84%E6%9B%B2%E7%8E%87%E5%8D%8A%E5%BE%84%E6%98%AF%E5%9C%86%E5%8D%8A%E5%BE%84%E5%90%97%3F)
设圆方程为y=√(R²-x²),(加不加负号一样的啊)
那么
y'= -x /√(R²-x²),(y')²=x²/(R²-x²)
y"= [-√(R²-x²) - x²/√(R²-x²)] / (R²-x²)
= -R²/(R²-x²)^(3/2)
而
曲率半径R'
=(1+y'²)^(3/2)/ |y"|
=[1+ x²/(R²-x²)]^(3/2) / [ R²/(R²-x²)^(3/2)]
=[ R²/(R²-x²)]^(3/2) / [ R²/(R²-x²)^(3/2)]
= R^3 /R²
=R
所以推出来曲率半径就是圆的半径
那么
y'= -x /√(R²-x²),(y')²=x²/(R²-x²)
y"= [-√(R²-x²) - x²/√(R²-x²)] / (R²-x²)
= -R²/(R²-x²)^(3/2)
而
曲率半径R'
=(1+y'²)^(3/2)/ |y"|
=[1+ x²/(R²-x²)]^(3/2) / [ R²/(R²-x²)^(3/2)]
=[ R²/(R²-x²)]^(3/2) / [ R²/(R²-x²)^(3/2)]
= R^3 /R²
=R
所以推出来曲率半径就是圆的半径