Please HeLp with definite integral

In summary, the conversation is about solving a definite integral of (1 + 3x) dx from (-1,5). The person is struggling to get the correct answer and suspects they may be using the wrong property or multiplying incorrectly. They are advised to show more of their working and reminded of the formula for indefinite integrals. The final solution should be 42.5.
  • #1
keltix
42
0

Homework Statement


definite integrals (1 + 3x) dx from (-1,5)





The Attempt at a Solution


i keep getting 6+54 but it should be 6+36

i think i might be using the wrong property

or multiplying wrong: 3[(6/n)i](6/n)
 
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  • #2
If you show more of your working it will make it easier for us to help you...
What do you get for the indefinite integral?
 
  • #3
If it helps, remember that
[tex] \int^{b}_{a} x^n dx = { \left[ \frac{x^{n+1}}{n} \right] }^b_a [/tex].
And as mda said, it would be helpful to know how your calculations look.
 
  • #4
the indefinite integral is " X + [tex]\frac{3}{2}[/tex]X[tex]^{2}[/tex] " and if you calculate it for 5 to -1 the answer must be 42
 
  • #5
If you integrate the function (3x+1) then it becomes (1.5x^2+x) where 5 is the upper limit and -1 is the lower. Sub in x=5 first, then minus the answer for x=-1 and you should end up with 42. When x=5 you should get 42.5, and when x=-1 you should get 0.5. Make sure that when you square -1 the calculator makes it 1, and does not leave it as -1 as some do.
 

1. What is a definite integral?

A definite integral is a mathematical concept used to find the exact area under a curve between two specific points on a graph. It is denoted by ∫ b to a f(x)dx, where a and b represent the lower and upper bounds of the integral, and f(x) is the function being integrated.

2. How do I solve a definite integral?

To solve a definite integral, you can use the fundamental theorem of calculus, which states that the definite integral of a function f(x) can be evaluated by finding its antiderivative F(x) and plugging in the upper and lower bounds. You can also use numerical methods or online integral calculators to find the solution.

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

While a definite integral has specific bounds and a definite numerical value, an indefinite integral does not have any bounds and represents a general solution in the form of a function. An indefinite integral is denoted by ∫ f(x)dx, and it can have multiple solutions with different constants of integration.

4. What are some real-world applications of definite integrals?

Definite integrals are used in various fields such as physics, engineering, and economics to calculate quantities such as work, displacement, area, and volume. For example, the definite integral of a velocity function can give the total distance traveled by an object.

5. Can I solve a definite integral without knowing the function?

Yes, you can approximate the value of a definite integral using numerical methods such as the trapezoidal rule or Simpson's rule. These methods use a series of calculated values from the function to approximate the area under the curve. However, for an exact solution, you will need to know the function and its antiderivative.

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