# Find a particular solution to the differential equation?

## Homework Statement

Find a particular solution to the differential equation
-6y''+5y'-1y
=
-1t^2+1t+1e^2t

y = y(c) + y(p)

## The Attempt at a Solution

First solve the homogeneous equation -6y" + 5y' - y = 0.
The characteristic equation is -6r^2 + 5r - 1 = 0 --> (1-2r)(1-3r) = 0 --> r = 1/2 or r = 1/3
So y(c) = Ae^(t/2) + Be^(t/3)
Now using methods of undetermined coefficients we assume y(p) = Ct^2 + Dt + E + Fe^(2t)
--> y'(p) = 2Ct + D + 2Fe^(2t)
--> y"(p) = 2C + 4Fe^(2t)
Substituting into the equation yields
LHS
= -6[2C + 4Fe^(2t)] + 5[2Ct + D + 2Fe^(2t)] - [Ct^2 + Dt + E + Fe^(2t)]
= -12C - 24Fe^(2t) + 10Ct + 5D + 10Fe^(2t) - Ct^2 - Dt - E - Fe^(2t)
= (-C)t^2 + (10C - D)t + (5D - E - 12C) + (-15F)e^(2t)
Comparing the coefficients on the LHS and RHS we have
-C = -1 --> C = 1
10C - D = 1 --> D = 9
5D - E - 12C = 0 --> E = 33
-15F = 1 -- F = -1/15
So y(p) = t^2 + 9t + 33 - (1/15)e^(2t)
Hence y = Ae^(t/2) + Be^(t/3) + t^2 + 9t + 33 - (1/15)e^(2t)

## Answers and Replies

NascentOxygen
Staff Emeritus
Science Advisor
You will find this gets moved over to the calculus forum.

By the way, do you have a question to ask, to accompany your working?