Is the sign of the integral of this function negative?

In summary, the conversation discusses a function f(x) that is continuous and differentiable on the interval [0,1), with a limit of positive infinity as x approaches 1 from the left. The function also has a finite integral A on the interval, and the question asks whether it is possible for the sign of A to be negative. An example is provided where f(x) is negative for much of the interval, implying that it is possible for the sign of A to be negative.
  • #1
Rlwe
18
1
Let ##f:[0;1)\to\mathbb{R}## and ##f\in C^1([0;1))## and ##\lim_{x\to1^-}f(x)=+\infty## and ##\forall_{x\in[0;1)}-\infty<f(x)<+\infty##. Define $$A:=\int_0^1f(x)\, dx\,.$$ Assuming ##A## exists and is finite, is it possible that ##\text{sgn}(A)=-1##?
 
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  • #2
f(x) < 0 for much of the interval.
 
  • #3
Rlwe said:
Let ##f:[0;1)\to\mathbb{R}## and ##f\in C^1([0;1))## and ##\lim_{x\to1^-}f(x)=+\infty## and ##\forall_{x\in[0;1)}-\infty<f(x)<+\infty##. Define $$A:=\int_0^1f(x)\, dx\,.$$ Assuming ##A## exists and is finite, is it possible that ##\text{sgn}(A)=-1##?
Try $$f(x)=\frac{1}{\sqrt{1-x}}-3.$$
 

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