4.9t²=20,t=?0.8t²=20 t=?
问题描述：
4.9t²=20,t=?0.8t²=20 t=?
答
4.9t²=20,t^2=200/49,t=±10√2/7
0.8t²=20 ,t^2=200/8=25,t=±5