1.

If f(x) and g(x) are continuous and differentiable functions, then prove that there exists c in [a,b] such that (f'(c))/(f(a)-f(c))+(g'(c))/(g(b)-g(c))=1.

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Solution :`(F'(c))/(f(a)-f(c))+(g'(c))/(g(b)-g(c))=1`
Put c = x
`rArr""(f'(x))/(f(x)-f(a))+(g'(x))/(g(x)-g(b))=-1`
`rArr""(d)/(dx)log_(E)(f(x)-f(a))+(d)/(dx)log_(e)(g(x)-g(b))=-1`
`rArr""d[(log_(e)(g(x)-f(a))(g(x)-g(b))]=-dx`
`rArr""(log_(e)(f(x)-f(a))(g(x)-g(b))]=-x+K`
`rArr""(f(x)-f(a))(g(x)-g(b))=e^(-x+k)`
`rArr""(f(x)-f(a))(g(x)-g(b))e^(x)-e^(k)=0`
Now let `H(x)=(f(x)-f(a))(g(x)-g(b))e^(x)-e^(k)`
`h(a)=h(b)=-e^(k)`
Then by ROLLE's Theorem, there exists atleast one `c in (a,b)` such that
`h'(c)=0`
`rArr""(f'(c))/(f(a)-f(c))+(g'(c))/(g(b)-g(c))=1`


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