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# physicsgirl

• ### Which of the following integrating factors makes the equation -xsinydx + (2+x)cosydy = 0 exact?

a. u = 1

b. u = x

c. u = e^x

d. u = (x+2)/e^x

• ### The form of the solution to 2(dy/dt) + 3y = e^-t , y(0)=5 is...?

a. Ae^-1.5t + Be^-t

b. Ae^-1.5t + Bte^-t

d. Ae^1.5t + Bte^-t

Mathematics7 years ago
• ### Which of the following apply to the equation xcos(y)y' + siny = 0?

a. linear, exact, not separable

b. linear, exact, separable

c. linear, separable, not exact

d. linear, not exact, not separable

e. nonlinear, exact, not separable

f. nonlinear, exact, separable

g. nonlinear, separable, not exact

h. nonlinear, not exact, not separable

Hint: it's definitely not d.

• ### Which of the following apply to the equation x^2 (dy/dx) + cosx + y = 0?

a. linear, exact, not separable

b. linear, exact, separable

c. linear, separable, not exact

d. linear, not exact, not separable

e. nonlinear, exact, not separable

f. nonlinear, exact, separable

g. nonlinear, separable, not exact

h. nonlinear, not exact, not separable

• ### Compute inverse Laplace transform of?

1. (2s+5)/s(s^2+1)

2. (2s^2+13s+5)/(s+3)(s-1)^2

• ### Compute the laplace transform of?

1. cost(t)sin(t)

2. cos^2(t)

Hint: first use trig identities.

• ### Can you help express the solution of the initial value problem in terms of a convolution integral?

y" + 2y' + 2y = sin(at), y(0)=0, y'(0)=0

y" + y' + (5/4)y = 1 - u_pi (t), y(0)=1, y'(0)=-1

• ### FInd the solution of the initial value problem?

y''' - 3y'' + 2y' = t + e^t

y(0) = 1

y'(0) = -1/4

y''(0) = -3/2

• ### FInd the solution of the initial value problem?

y''' - y'' + y' - y = 0

y(0) = 2

y'(0) = -1

y''(0) = -2

I'm mainly stuck on how to get the r values from the characteristic equation.

[The answer is: y = 2cos(t) - sin(t) ]

• ### Find the general solution of the differential equations?

1) y" + y = tan(t), 0 < t < pi/2. [The answer is y= c1cos(t) + c2sin(t) - (cos(t)) ln(tan(t) + sec(t))]

2) y" - 5y' +6y = g(t), where g is an arbitrary continuous function. [The answer is y=c1e^2t + c2e^3t + integral[e^3(t-s) - e^2(t-s)]g(s)ds]

• ### Solve the initial value problem: 9y" - 12y' + 4y = 0, y(0) = 2, y'(0) = -1?

The answer is y = 2e^(2t/3) - (7/3)te^(2t/3), but I'm having trouble getting there.

I know that r1 = 2/3 = r2, so there are repeated roots.

Then I was using y = v(t) e^(2t/3), y' = v'(t) e^(2t/3) + (2/3)v'(t)e^(2t/3)

I was having trouble finding y".

Then I would sub that back into the original equation.

Is that right? And where do I go from here?

• ### FInd the solution of the initial value problem?

y" + 2y' + 2y = 0, y(pi/4) = 2, y(pi/4) = -2

• ### Find the general solution of differential equation?

y" - 3y' + 2y = 2e^t

• ### How do I make Siri autocorrect certain words?

For instance, whenever I say "sail" when I'm reading a text, she types "sale". How do I get her to autocorrect "sale" to "sail"?

I already tried putting a shortcut in the keyboard shortcut settings that autocorrects "sale" to "sail" when I am typing out a text. However when I'm using Siri to type m texts for me, she doesn't autocorrect the word..HELP!

1 AnswerMedia & Journalism8 years ago
• ### Find the general solution of the following differential equations:?

1. y" + y = tant, 0<t<pi/2

2. y" - 5y' + 6y = g(t)