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Let `f`be a continuous function on `[a ,b]dot`Prove that there exists a number `x in [a , b]`such that`int_a^xf(t)dx=int_x^bf(t)dtdot` |
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Answer» Let `g(x)=int_(a)^(x)f(t)dt-int_(x)^(b)f(t)dt, xepsilon[a,b]` We have `g(a)=int_(a)^(b)f(t)dt` and `g(b)=int_(a)^(b)f(t)dt` `:.g(a).g(b)=-[int_(a)^(b)f(t)dt]^(2)le0` clearly `g(x)` is continuous in `[a,b]` an `g(a).g(b)le0` It implies that `g(x)` will become zero at least once in `[a,b]`. Hence `int_(a)^(x)f(t)dt=int_(x)^(b)f(t)dt` for all least one value of `xepsilon[a,b]` |
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