let f be continuos in [a,b] and differentiable in (a,b) show that

$\displaystyle

\frac{{af(b) - bf(a)}}

{{b - a}} = x_0 f'(x_0 ) - f(x_0 )

$

for some Xo

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i tried by defining g(x)= (a+b-X)f(X)

then using the mean value theorem on g(x) i try to solve the problem but i get stuck D: plz help me