How to fit regression model in R-CodePudding

I am attempting to do the following question and am stuck on part 1 where I am asked to fit the regression model and interpret the results. I was taught how to do this for a model with just B1 and linear (t-1978), but now with B2(t-1978)^2 I am confused how to do it?

library(climate) #R package of choice for Time series module
trend= time(co2) - 1978
#Turn months to factors
M = factor(cycle(co2))
reg = lm(co2 ~  time ( co2 )   I( time (co2)^2)   trend   M,
    na.action = NULL)
summary(reg)

I have tried the above and my trend is NA so it is clearly wrong

CodePudding user response：

You seem pretty close (I was very confused by the cycle(co2), time(co2) calls, which are working with ts objects. If I put in trend instead of time(co2) I get sensible answers ...

reg = lm(co2 ~  trend   I(trend^2)   M, na.action = NULL)