MHB How to Evaluate the Given Definite Integral?

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The discussion revolves around evaluating the definite integral of a continuous and differentiable function f, given a specific condition involving a summation. The integral to be evaluated is from 0 to 11, and the options for the answer include expressions involving e and natural logarithms. An initial attempt to define f as |e^x - 11| was unsuccessful in yielding the correct integral value. A key hint suggests breaking the integral into segments and utilizing properties of definite integrals to simplify the evaluation process. The correct answer to the integral is identified as option A, 65 + 4ln2 - 7e.
Saitama
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Problem:
If f is continuous and differentiable function in $x \in (0,1)$ suuch that $\sum_{r=0}^{1}\left(f(x+r)-\left|e^x-r-1\right|\right)$=0, then $\int_0^{11} f(x)\,dx$ is

A)65+4ln2-7e
B)63+4ln2-9e
C)69-9e
D)29-23e

Ans: A

Attempt:
I could only write the following:
$$f(x)+f(x+1)+\cdots+f(x+11)=|e^x-1|+|e^x-2|+\cdots+|e^x-11|$$
Since I had no idea how to proceed further, I assumed $f(x)=|e^x-11|$ but evaluating the definite integral with this f(x) doesn't give the right answer.

Any help is appreciated. Thanks!
 
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Hint: you can write the integral as

$$\int^1_0+\int^2_1 + \cdots +\int^{11}_{10} f(x) \, dx$$

Then $$\int^2_1 f(x) \, dx = \int^1_0 f(x+1) \, dx $$
 
ZaidAlyafey said:
Hint: you can write the integral as

$$\int^1_0+\int^2_1 + \cdots +\int^{11}_{10} f(x) \, dx$$

Then $$\int^2_1 f(x) \, dx = \int^1_0 f(x+1) \, dx $$

Ah, how could I miss that. :p

Thanks a lot ZaidAlyafey! :)
 
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