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## Homework Statement

4y'' + y = cosx

Solve using variation of parameters

## Homework Equations

## The Attempt at a Solution

from a) -> yc(x) = c1cos(x/2) + c2sin(x/2)

let y1 = cos(x/2) , y2 = sin(x/2)

y1y2' - y2y1' = 1/2cos

^{x/2}+ 1/2sin

^{x/2}= 1/2

u1' = ???

How do I find this?