Printed Page 1061
1061
Concepts and Vocabulary
The differential equation d2ydx2+5(dydx)3−y=0 is of order _________ and degree ________.
2; 1
True or False The differential equation (x2+2)dydx−1xy=0 is linear.
True
True or False y=−4x2+100 is a solution of the differential equation dydx=−8x.
True
True or False y=8e5x is a solution of the differential equation dydx+3=8e5x.
False
Skill Building
In Problems 5–14, state the order and degree of each equation. State whether the equation is linear or nonlinear.
dydx+x2y=xex
This is a first-order differential equation of degree 1. The differential equation is linear.
d3ydx3+4d2ydx2−5dydx+3y=sinx
d4ydx4+3d2ydx2+5y=0
This is a fourth-order differential equation of degree 1. The differential equation is linear.
d2ydx2+ysinx=0
d2ydx2+xsiny=0
This is a second-order differential equation of degree 1. The differential equation is nonlinear.
d6xdt6+d4xdt4+d3xdt3+x=t
(drds)2=(d2rds2)3+1
This is a second-order differential equation of degree 3. The differential equation is nonlinear.
x(y′′)3+(y′)4−y=0
d2yds2+3sdyds=y
This is a second-order differential equation of degree 1. The differential equation is linear.
dydx=1−xy+y2
In Problems 15–22, show that the function y is a solution of the differential equation.
y=ex+3e−x,d2ydx2−y=0
See Student Solutions Manual.
y=5sinx+2cosx,d2ydx2+y=0
y=sin(2x),d2ydx2+4y=0
See Student Solutions Manual.
y=cos(2x),d2ydx2+4y=0
y=31−x3,dydx=x2y2
See Student Solutions Manual.
y=1+Ce−x2/2,dydx+xy=x, C is a constant
y=e−2x,y′′+3y′+2y=0
See Student Solutions Manual.
y=ex,2y′′+y′−3y=0
In Problems 23–30, use implicit differentiation to show that the given equation is a solution of the differential equation. C is a constant.
y2+2xy−x2=C,dydx=x−yx+y
See Student Solutions Manual.
x2−y2=Cx2y2,dydx=y3x3(Hint: Solve for C first.)
x2−y2=Cx,dydx=x2+y22xy (Hint: Solve for C first.)
See Student Solutions Manual.
x2y+12x2+16y=9,dydx=−2xy+24xx2+16
2(x−1)ex+y2=C,dydx=−xexy
See Student Solutions Manual.
x2−y2+2(e−x−ey)=C,dydx=x−e−xy+ey
tan−1y=x+x22+C,dydx=xy2+y2+x+1
See Student Solutions Manual.
1+2y2√1+x2=Cy2,dydx=xy3√1+x2 (Hint: Solve for C first.)
Applications and Extensions
In Problems 31–34, for each differential equation, show that y is a particular solution that satisfies the initial condition.
dydx=yx;y=3x initial condition: y=3 when x=1
See Student Solutions Manual.
dydx=3y;y=2e3x initial condition: y=2 when x=0
dydx=y2;y=11−x initial condition: y=1 when x=0
See Student Solutions Manual.
xdydx+y=x2;y=x23+3x initial condition: y=4 when x=3
In Problems 35–38, show that y is a solution of the differential equation.
y=C1eax+C2e−ax,d2ydx2−a2y=0, C1, C2 are constants
See Student Solutions Manual.
y=sinhx,d2ydx2=y
y=a2kt1+akt,dydt=k(a−y)2, a>0, and k are constants
See Student Solutions Manual.
y=ln(C−e−x),dydx=e−(x+y), C is a constant
Find the values of n so that y=enx is a solution of y′′+y′−6y=0
n=−3,2
Find a first-order differential equation that has y=ex+e−x as a solution.
Schrödinger Equation In quantum mechanics, the time-independent Schrödinger equation in one dimension can be written as −h22md2Y(x)dx2+U(x)Y(x)=EY(x). What are the degree and order of this differential equation?
The Schrödinger equation is a second-order differential equation of degree 1.