0.002x² + 0.01x =30
等式两边同时乘以500得：
x² + 5x - 15000 = 0
(x -120)(x + 125) = 0
x = 120 或 x = -125
一道二次函数关系式怎么解?0.002x的平方+0.01x=30
0.002x² + 0.01x =30
等式两边同时乘以500得：
x² + 5x - 15000 = 0
(x -120)(x + 125) = 0
x = 120 或 x = -125