解方程：30t-0.5*0.25*t^2=1800

解方程：30t-0.5*0.25*t^2=1800
解方程：30t-0.5*0.25*t^2=1800

解方程：30t-0.5*0.25*t^2=1800
30t-0.5*0.25*t^2=1800
30t-0.125t²=1800
240t-t²=14400
t²-240t+120²=0
(t-120)²=0
t=120

解方程：30t-0.5*0.25*t²=1800
两边同乘以8，得240t-t²=14400
移项得t²-240t+14400=(t-120)²=0，故得t=120.

30t-0.125t^2＝1800
0 .125t^2＝30t－1800
t^2＝(30t-1800)*0.125
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t＝√3.75t-225