# 26 Lecture

## MTH101

### Midterm & Final Term Short Notes

## Integration by Substitution

Integration by substitution is a powerful technique used in calculus to simplify and evaluate complex integrals. It is also known as u-substitution, and it involves changing the variable of integration by using a substitution.

**Important Mcq's**

Midterm & Finalterm Prepration

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**What is the main goal of integration by substitution?**

A) To simplify complex integrals

B) To differentiate functions

C) To solve differential equations

D) To find limits of functions

Answer: A

**What is the general formula for integration by substitution?**

A) ?f(x)dx = F(x) + C

B) ?f(g(x))g'(x)dx = ?f(u)du

C) ?f'(x)dx = f(x) + C

D) ?e^x dx = e^x + C

Answer: B

**What should be substituted in the integral ?x^2 e^(x^3) dx using integration by substitution?**

A) x

B) e^(x^3)

C) x^3

D) 1/x

Answer: C

**How do you evaluate the integral after making the substitution?**

A) Apply the chain rule

B) Use trigonometric identities

C) Use integration by parts

D) Use standard integration rules

Answer: D

**What is the derivative of the function u = sin(x)?**

A) cos(x)

B) sin(x)

C) -cos(x)

D) -sin(x)

Answer: A

**What is the substitution used for the integral ?x/(x^2+1) dx?**

A) u = x^2

B) u = x^2+1

C) u = x^3

D) u = x/(x^2+1)

Answer: D

**Can you use integration by substitution to evaluate definite integrals?**

A) Yes

B) No

Answer: A

**What is the importance of adjusting the limits of integration when using integration by substitution?**

A) To simplify the integral

B) To make the integral more complex

C) To ensure that we are integrating over the same range in terms of the new variable

D) To evaluate the integral faster

Answer: C

**What is the substitution used for the integral ?e^(2x+1) dx?**

A) u = 2x

B) u = 2x+1

C) u = e^(2x+1)

D) u = e^(2x)

Answer: B

**Can you use integration by substitution for all integrals?**

A) Yes

B) No

Answer: B

**Subjective Short Notes**

Midterm & Finalterm Prepration

Past papers included

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**What is integration by substitution?**

**Answer:** Integration by substitution is a technique used in calculus to simplify and evaluate complex integrals by changing the variable of integration using a substitution.

**How do you find the right substitution for integration by substitution?**

**Answer:** The key to finding the right substitution is to look for a function u that is a composite of the function inside the integral and its derivative, such that du = f'(x)dx.

**What is the general formula for integration by substitution?**

**Answer: **The general formula is ?f(g(x))g'(x)dx = ?f(u)du, where u = g(x).

**How do you evaluate the integral after making the substitution?**

**Answer:** After making the substitution, we use standard integration rules to evaluate the integral in terms of the new variable, u.

**Can you use integration by substitution to evaluate definite integrals?**

**Answer:** Yes, but you need to adjust the limits of integration based on the substitution you have made.

**What is the purpose of integration by substitution?**

**Answer: **The purpose is to simplify complex integrals and make them easier to evaluate using standard integration rules.

**Can you use integration by substitution for all integrals?**

**Answer:** No, but it is a powerful technique that can be used for many integrals involving composite functions, trigonometric functions, and other complex functions.

**Why is integration by substitution sometimes called u-substitution?**

**Answer: **It is called u-substitution because we typically use the variable u to represent the substitution.

**What are some common substitutions used in integration by substitution?**

**Answer:** Some common substitutions include u = g(x), u = sin(x), and u = e^x.

**What is the importance of adjusting the limits of integration when using integration by substitution?**

**Answer:** It is important to adjust the limits of integration because the new variable, u, may have a different range than the original variable, x. By adjusting the limits of integration, we ensure that we are integrating over the same range in terms of the new variable, u.

### Integration by Substitution

Integration by substitution is a powerful technique used in calculus to simplify and evaluate complex integrals. It is also known as u-substitution, and it involves changing the variable of integration by using a substitution. This technique is particularly useful when the integrand involves a complex function, a composite function, or a trigonometric function. The idea behind integration by substitution is to use a substitution that will simplify the integrand and make it easier to integrate. To do this, we need to find a function u that is a composite of the function inside the integral and its derivative, such that du = f'(x)dx. We then substitute u for the function inside the integral, and replace dx with du/f'(x). This effectively changes the variable of integration from x to u, making it easier to integrate. Let's consider an example to see how this works. Suppose we want to evaluate the integral of x(1+x^2)^4 dx. This integrand involves a composite function (1+x^2)^4, which makes it difficult to integrate directly. To simplify the integrand, we can use the substitution u = 1+x^2. This means that du/dx = 2x, or dx = du/2x. We can substitute these expressions into the integral, to get: ?x(1+x^2)^4 dx = ?(u-1)(u)^4(du/2x) = (1/2)?(u^5 - u^4)du = (1/12)(1+x^2)^5 + C Here, we have simplified the integrand by substituting u = 1+x^2, and then evaluated the integral using standard integration rules. The constant of integration, C, is added to the end, since we are finding an indefinite integral. It is important to note that when we change the variable of integration using substitution, we also need to change the limits of integration. This is because the new variable, u, may have a different range than the original variable, x. To do this, we substitute the limits of integration into the substitution and then evaluate them in terms of the new variable, u. For example, if the original limits of integration are a and b, we can substitute them into the substitution to get: u(a) = 1+a^2 u(b) = 1+b^2 We can then evaluate the integral in terms of u, and substitute back in the original variable, x, to get the final answer. Integration by substitution is a powerful technique that can be used to evaluate a wide range of integrals. It is particularly useful for integrands involving composite functions, trigonometric functions, and other complex functions. The key to success with this technique is finding the right substitution to simplify the integrand. This may require some creativity and experimentation, but with practice, it becomes easier to recognize the right substitution for a given problem.**In summary,**integration by substitution is a powerful technique used in calculus to simplify and evaluate complex integrals. It involves changing the variable of integration by using substitution and then using standard integration rules to evaluate the integral. This technique is particularly useful for integrands involving composite functions, trigonometric functions, and other complex functions. With practice, it becomes easier to recognize the right substitution for a given problem and to use this technique to find the solution.