Chapter 8: Problem 11
Solve the following initial value problems. $$y^{\prime}(t)=3 y-6, y(0)=9$$
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Chapter 8: Problem 11
Solve the following initial value problems. $$y^{\prime}(t)=3 y-6, y(0)=9$$
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A differential equation of the form \(y^{\prime}(t)=f(y)\) is said to be autonomous (the function \(f\) depends only on \(y\) ). The constant function \(y=y_{0}\) is an equilibrium solution of the equation provided \(f\left(y_{0}\right)=0\) (because then \(y^{\prime}(t)=0\) and the solution remains constant for all \(t\) ). Note that equilibrium solutions correspond to horizontal lines in the direction field. Note also that for autonomous equations, the direction field is independent of t. Carry out the following analysis on the given equations. a. Find the equilibrium solutions. b. Sketch the direction field, for \(t \geq 0\). c. Sketch the solution curve that corresponds to the initial condition \(y(0)=1\). $$y^{\prime}(t)=\sin y$$
Determine whether the following equations are separable. If so, solve the initial value problem. $$y^{\prime}(t)=e^{t y}, y(0)=1$$
Determine whether the following statements are true and give an explanation or counterexample. a. The general solution of \(y^{\prime}(t)=2 y-18\) is \(y(t)=2 e^{2 t}+9\) b. If \(k>0\) and \(b>0,\) then \(y(t)=0\) is never a solution of \(y^{\prime}(t)=k y-b\) c. The equation \(y^{\prime}(t)=t y(t)+3\) is separable and can be solved using the methods of this section. d. According to Newton's Law of Cooling, the temperature of a hot object will reach the ambient temperature after a finite amount of time.
Consider the first-order initial value problem \(y^{\prime}(t)=a y+b, y(0)=A,\) for \(t \geq 0,\) where \(a, b,\) and \(A\) are real numbers. a. Explain why \(y=-b / a\) is an equilibrium solution and corresponds to a horizontal line in the direction field. b. Draw a representative direction field in the case that \(a>0\) Show that if \(A>-b / a,\) then the solution increases for \(t \geq 0\) and if \(A<-b / a,\) then the solution decreases for \(t \geq 0\). c. Draw a representative direction field in the case that \(a<0\) Show that if \(A>-b / a,\) then the solution decreases for \(t \geq 0\) and if \(A<-b / a,\) then the solution increases for \(t \geq 0\).
The reaction of certain chemical compounds can be modeled using a differential equation of the form \(y^{\prime}(t)=-k y^{n}(t),\) where \(y(t)\) is the concentration of the compound for \(t \geq 0, k>0\) is a constant that determines the speed of the reaction, and \(n\) is a positive integer called the order of the reaction. Assume that the initial concentration of the compound is \(y(0)=y_{0}>0\). a. Consider a first-order reaction \((n=1)\) and show that the solution of the initial value problem is \(y(t)=y_{0} e^{-k t}\). b. Consider a second-order reaction \((n=2)\) and show that the solution of the initial value problem is \(y(t)=\frac{y_{0}}{y_{0} k t+1}\). c. Let \(y_{0}=1\) and \(k=0.1 .\) Graph the first-order and secondorder solutions found in parts (a) and (b). Compare the two reactions.
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