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16.1 Assess Your Understanding

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1061

Concepts and Vocabulary

  1. The differential equation d2ydx2+5(dydx)3y=0 is of order _________ and degree ________.

2; 1

  1. True or False The differential equation (x2+2)dydx1xy=0 is linear.

True

  1. True or Falsey=4x2+100 is a solution of the differential equation dydx=8x.

True

  1. True or Falsey=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.

  1. dydx+x2y=xex

This is a first-order differential equation of degree 1. The differential equation is linear.

  1. d3ydx3+4d2ydx25dydx+3y=sinx

  1. d4ydx4+3d2ydx2+5y=0

This is a fourth-order differential equation of degree 1. The differential equation is linear.

  1. d2ydx2+ysinx=0

  1. d2ydx2+xsiny=0

This is a second-order differential equation of degree 1. The differential equation is nonlinear.

  1. d6xdt6+d4xdt4+d3xdt3+x=t

  1. (drds)2=(d2rds2)3+1

This is a second-order differential equation of degree 3. The differential equation is nonlinear.

  1. x(y)3+(y)4y=0

  1. d2yds2+3sdyds=y

This is a second-order differential equation of degree 1. The differential equation is linear.

  1. dydx=1xy+y2

In Problems 15–22, show that the function y is a solution of the differential equation.

  1. y=ex+3ex,d2ydx2y=0

See Student Solutions Manual.

  1. y=5sinx+2cosx,d2ydx2+y=0

  1. y=sin(2x),d2ydx2+4y=0

See Student Solutions Manual.

  1. y=cos(2x),d2ydx2+4y=0

  1. y=31x3,dydx=x2y2

See Student Solutions Manual.

  1. y=1+Cex2/2,dydx+xy=x, C is a constant

  1. y=e2x,y+3y+2y=0

See Student Solutions Manual.

  1. y=ex,2y+y3y=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.

  1. y2+2xyx2=C,dydx=xyx+y

See Student Solutions Manual.

  1. x2y2=Cx2y2,dydx=y3x3(Hint: Solve for C first.)

  1. x2y2=Cx,dydx=x2+y22xy (Hint: Solve for C first.)

See Student Solutions Manual.

  1. x2y+12x2+16y=9,dydx=2xy+24xx2+16

  1. 2(x1)ex+y2=C,dydx=xexy

See Student Solutions Manual.

  1. x2y2+2(exey)=C,dydx=xexy+ey

  1. tan1y=x+x22+C,dydx=xy2+y2+x+1

See Student Solutions Manual.

  1. 1+2y21+x2=Cy2,dydx=xy31+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.

  1. dydx=yx;y=3x initial condition: y=3 when x=1

See Student Solutions Manual.

  1. dydx=3y;y=2e3x initial condition: y=2 when x=0

  1. dydx=y2;y=11x initial condition: y=1 when x=0

See Student Solutions Manual.

  1. 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.

  1. y=C1eax+C2eax,d2ydx2a2y=0, C1, C2 are constants

See Student Solutions Manual.

  1. y=sinhx,d2ydx2=y

  1. y=a2kt1+akt,dydt=k(ay)2, a>0, and k are constants

See Student Solutions Manual.

  1. y=ln(Cex),dydx=e(x+y), C is a constant

  1. Find the values of n so that y=enx is a solution of y+y6y=0

n=3,2

  1. Find a first-order differential equation that has y=ex+ex as a solution.

  1. 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.