经济颖测方 (2),=a+b+cr2 ∑=mn++∑ =a∑t+b∑2+∑ 2y=a∑2+b∑+c∑t (3)v,=a+bt+ct+dt ∑=m+bc++ ∑=at+b2+c∑+∑ ∑=a∑2+b+c∑+∑ +b∑+c∑+d∑经济预测与决策方法        = + + = + + = + +            2 2 3 4 2 3 2 t y a t b t c t t y a t b t c t y na b t c t t t t 2 (2)y ˆ a bt ct t = + +        = + + + = + + + = + + + = + + +                    3 3 4 5 6 2 2 3 4 5 2 3 4 2 3 t y a t b t c t d t t y a t b t c t d t t y a t b t c t d t y na b t c t d t t t t t 2 3 (3) y ˆ a bt ct dt t = + + +