9t+0.5t^2=380
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9t+0.5t^2=3809t+0.5t^2=3809t+0.5t^2=3809t+0.5t^2=380t^2+18t=760t^2+18t+81=760+81=841(t+9)^2=(±29)^2t
9t+0.5t^2=380
9t+0.5t^2=380
9t+0.5t^2=380
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
20或-38 公式法啊
t1=20 t2=-38
9t+0.5t^2=380
方程可化为
t²+18t-760=0
(t+38)(t-20)=0
t1=-38,t2=20
t=901