integration proof (1 Viewer)

[megan09]

hi,
there is a common proof that has come up quite often in past trial and hsc questions :
prove:
a a
{ f(x) dx = { f(a-x) dx
0 0

which i understand as you just use the substitution x= a-u
i was just wandering if you need a reason for the line in the proof:



a a
{ f(a-u) du = { f(a-x) dx
0 0

and if so what would that reason be?
i was thinking along the lines of
'since x and u are independent variables'

 

[annabackwards]

You don't need a reason as sikhman said, but the reason is because "a" and "u" are dummy values ie pronumerals.

 

[Trebla]

Just say "u is a dummy variable"
done.