Example Newton's law of cooling may be stated in this way:The time rate of change (the rate of change with respect to t)of the temperature T(t)of a body is proportional to the difference between T and the temperature A of the surrounding medium. That is dT =-k(T-A), dr where k is a positive constant.Observe that If T>A,then dT/dt<0,T is decreasing If T<A,then dT/dt>0,T is increasing 4口14①y至，元2000 Peipei Shang School of Mathematical Sciences shang@tongji.edu.Ordinary Differential EquationsExample Newton’s law of cooling may be stated in this way: The time rate of change (the rate of change with respect to t) of the temperature T(t) of a body is proportional to the difference between T and the temperature A of the surrounding medium. That is dT dt = −k(T −A), where k is a positive constant. Observe that If T > A, then dT/dt < 0, T is decreasing If T < A, then dT/dt > 0, T is increasing Peipei Shang School of Mathematical Sciences shang@tongji.edu.cn Ordinary Differential Equations