求翻译：（2）式的预测模型与一般的线性趋势模型的区别在于，式中 、 是参数变量，随着时间自变量 的变化而变化，即直线在各时期的截距和斜率是可能不同的； 是从 期开始的预测期数。是什么意思？

(2) prediction model and the difference of the linear trend model is, where is the parameter variables change over time since the change of variables, that is, the intercept and slope of the straight line in each period may be different; from the beginning of the forecast number of installments.

(2) the forecast model and a general linear trend model, the difference is in the variable parameters, and, over time, which changes of the argument in a straight line, that is the period of the intercept and slope are may be different; and it is from the start of the forecast period.

(2) -like forecast model and the general linear tendency model difference lies in, in the formula, is the parameter variable, changes along with the time independent variable change, namely the straight line in various times intercept and the slope is possible different; Is forecast time number whi

(2) forecast model with difference between general linear trend model, type, parameter variables, change as the time since the change of variables, that is linear in each period the intercept and slope may be different; number of forecast period is from the period beginning.

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