How to Evaluate the Given Definite Integral?

In summary, the problem states that if f is a continuous and differentiable function in the interval (0,1) and satisfies the given sum, then the definite integral of f from 0 to 11 has four possible values (A, B, C, D). In attempting to solve the problem, the person tried to use the given sum to express the definite integral as a sum of integrals from 0 to 1, 1 to 2, and so on up to 10 to 11. However, they were unable to solve it and suggested a possible function of f(x) as |e^x-11|. Further help was provided by using the property of definite integrals to express f(x+1)
  • #1
Saitama
4,243
93
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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  • #2
Hint: you can write the integral as

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

Then \(\displaystyle \int^2_1 f(x) \, dx = \int^1_0 f(x+1) \, dx \)
 
  • #3
ZaidAlyafey said:
Hint: you can write the integral as

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

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

Ah, how could I miss that. :p

Thanks a lot ZaidAlyafey! :)
 

FAQ: How to Evaluate the Given Definite Integral?

What is a definite integral?

A definite integral is a mathematical concept used to find the total area under a curve on a given interval. It involves adding up an infinite number of infinitely small rectangles to get an accurate measurement of the area.

How do you evaluate a definite integral?

To evaluate a definite integral, you first find the indefinite integral of the function being integrated. Then, plug in the upper and lower limits of the interval into the indefinite integral and subtract the result to get the final value.

What is the difference between a definite and indefinite integral?

The main difference between a definite and indefinite integral is that a definite integral has specific upper and lower limits, while an indefinite integral does not. A definite integral also gives a numerical value, whereas an indefinite integral gives a function.

Why is it important to evaluate definite integrals?

Evaluating definite integrals is important because it allows us to find the exact area under a curve, which can be applied to real-world situations. It is also a fundamental concept in many branches of mathematics and physics, such as calculus and mechanics.

What are some common methods for evaluating definite integrals?

Some common methods for evaluating definite integrals include substitution, integration by parts, and using special trigonometric identities. The choice of method depends on the complexity of the function being integrated and the techniques that have been covered in the course or subject.

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