Evaluate the definite integral

In summary, the conversation discusses how to evaluate the definite integral \int Sin(3t) dt with boundaries Pi/3 and zero. Initially, there is a mistake in the attempt at a solution, but after discussing substitutions and the general integration formula for Sine, it is determined that the correct answer is -cos(3t)/3 with a constant.
  • #1
jimen113
67
0
[SOLVED] Evaluate the definite integral

1. Homework Statement
[tex]\int[/tex] Sin(3t) dt; the boundaries are Pi/3 and zero.

Homework Equations





The Attempt at a Solution


3-cos(pi/3)[tex]^{}2[/tex]-cos(0)= not the correct answer.
Help!
 
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  • #2
Do a substitution: x = 3t. if you do that, then what does dt = ?
Plug x in, what's the integral of sinx?
 
  • #3
If x=3t, then
dt=3
integral of sin x is -cos x
Is this correct?
 
  • #4
jimen113 said:
If x=3t, then
dt=3
integral of sin x is -cos x
Is this correct?
There is no substitution required (although that would yield the same answer).
Just look at the general integration formula for Sine:
[tex]\int\sin nx\dx=- \frac{\cos nx}{n} + \mbox{Constant}[/tex]
Can you get the answer now?
 
  • #5
jimen113 said:
If x=3t, then
dt=3
integral of sin x is -cos x
Is this correct?

If x= 3t, then dx= 3dt so dt= (1/3)dx. "dt= 3" doesn't make any sense- a differential is not a number!
 
  • #6
Thank you HallsofIvy, Reshma, & Izkelley for your help. I realized my mistake was: "dt=3"
 

Related to Evaluate the definite integral

1. What is a definite integral?

A definite integral is a mathematical concept that represents the area under a curve between two points on a graph. It is denoted by the symbol ∫ and is used to calculate the total accumulation of a function over a specific interval.

2. How is a definite integral evaluated?

To evaluate a definite integral, you need to first determine the limits of integration (the two points on the graph) and then use the fundamental theorem of calculus to find the antiderivative of the function. Next, substitute the limits of integration into the antiderivative and calculate the resulting value.

3. What is the difference between a definite and indefinite integral?

A definite integral has specific limits of integration and results in a single numerical value, while an indefinite integral does not have limits of integration and results in a function. In other words, a definite integral gives a specific answer, while an indefinite integral gives a family of answers.

4. What are some practical applications of definite integrals?

Definite integrals are used in many fields of science and engineering, such as physics, economics, and statistics. They can be used to calculate areas, volumes, and other physical quantities, as well as to model real-world phenomena like population growth and changes in stock prices.

5. Can definite integrals be evaluated using numerical methods?

Yes, definite integrals can be evaluated using numerical methods such as the trapezoid rule, Simpson's rule, and Monte Carlo integration. These methods are used when the function is too complex to find an exact solution or when the limits of integration are difficult to work with.

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