9t+0.5t^2=380
问题描述：
9t+0.5t^2=380
答
9t+0.5t^2=380
t^2+18t=760
t^2+18t+81=760+81=841
(t+9)^2=(±29)^2
t+9=±29
t=-9±29
t=-38,t=20