请问为什么不考虑b1b2是否等于零？

问题如下：

Mike is to develop a model to predict future quarterly sales. He begins by running the following regression: ln Sales_t – ln Sales_t–1 = b₀ + b₁(ln Sales_t–1 – ln Sales_t–2) + b₂(ln Sales_t–4 – ln Sales_t–5)+ε_t.

Based on the regression output in Exhibit, the forecasted value of quarterly sales for March 2016 is closest to:

选项：

A.

$4.193 billion

B.

$4.205 billion

C.

$4.231 billion

解释：

The quarterly sales for March 2016 is calculated as follows:

lnSales_t – ln Sales_t–1 = b₀ + b₁(ln Sales_t–1 – ln Sales_t–2) + b₂(ln Sales_t–4 – lnSales_t–5).

lnSales_t – ln 3.868 = 0.0092 – 0.1279(ln 3.868 – ln 3.780) + 0.7239(ln 3.836– ln 3.418).

lnSales_t – 1.35274 = 0.0092 – 0.1279(1.35274 – 1.32972) +0.7239(1.34443 – 1.22906).

lnSales_t = 1.35274 + 0.0092 – 0.1279(0.02301) + 0.7239(0.11538).

lnSales_t= 1.44251.

Sales_t = e^1.44251 = 4.231.