T0 = 36  # °C
TA = 20  # °C
tau = 10 # h

curve(TA + (T0 - TA)*exp(-t/tau), 0, 6*tau, xname='t',col='red',
      xlab = 't (h)', ylab='T (°C)', ylim=c(0,T0) )
grid()
for(i in 0:6) {
points(i*tau, TA + (T0 - TA)*exp(-i*tau/tau), col='red', pch=19)
}