source('../../Data/data_loaders.R')

DF = load_particle_board_data()

m = lm( strength ~ temperature + I(temperature^2), data=DF )
summary(m)

c = coefficients(m)
-c[2]/(2*c[3])

#postscript("../../WriteUp/Graphics/Chapter2/ex_2_15_plot.eps", onefile=FALSE, horizontal=FALSE)
plot( DF$temperature, DF$strength, type='p', xlab='temperature', ylab='strength' )
points( DF$temperature, m$fitted, type='l', col='green')
grid()
#dev.off()