Calculating Wronskian for u and v: f+3g and f-g

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The Wronskian of functions u = f + 3g and v = f - g can be derived from the known Wronskian of f and g, which is given as W(f, g) = tcos(t) - sin(t). To find W(u, v), the expression W(u, v) = (f + 3g)(f - g)' - (f + 3g)'(f - g) must be expanded. The derivatives involved are (f - g)' = f' - g' and (f + 3g)' = f' + 3g'. Utilizing properties of determinants can simplify the calculation of W(u, v) in terms of simpler Wronskians.

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If the Wronskian of f and g is tcos(t)-sin(t), and if u=f+3g, v=f-g, find the Wronskian of u and v.

W=fg'-gf'
(f+3g)(f-g)'-(f+3g)'(f-g)
What's next?
 
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Success said:
If the Wronskian of f and g is tcos(t)-sin(t), and if u=f+3g, v=f-g, find the Wronskian of u and v.

W=fg'-gf'
(f+3g)(f-g)'-(f+3g)'(f-g)
What's next?
You have fg' - gf' = tcos(t)-sin(t).

I would expand (f+3g)(f-g)'-(f+3g)'(f-g) to see what that does. (f - g)' is just f' - g', and similar for (f + 3g)'.
 
It would be easier to use properties of determinants. For example, what is W(u+v,g) in general for any u and v in terms of simpler Wronskians.
 

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