Find the area between f(x) = 3x^2 + 2x and x= 1 and x= 2

4 Answers | Add Yours

hala718's profile pic

hala718 | High School Teacher | (Level 1) Educator Emeritus

Posted on

f(x) = 3x^2 + 2x and x= 1 and x= 2

First we need to find the difinet integral for f(x) between (1,2)

Let F (x) = intg f(x)

==> F(x) = intg 3x^2 + 2x  dx

                = intg 3x^2 dx  + intg 2x dx

                 = 3x^3/3 + 2x2 /2 + C

                  = x^3 + x^2 + C

Now the area is:

A = F(2) - F(1)

   = 2^3 + 2^2 + C - (1^3 + 1^2 + C)

     = 8 + 4 + C - 1 -1 - c

      = 10

Then the area between f(x) and x= 1 and x= 2 is:

A = 10

neela's profile pic

neela | High School Teacher | (Level 3) Valedictorian

Posted on

The area under  the curve f(x) and between  x= a and x = b is given by:

Area = Int f(x) dx from x= a to x = b.

 Area = Int {3x^2+2x} dx from x = 1 to x = 2.

Area = {(3x^3/3+2x^2/2 +C)at  x= 2 } - {(3x^3/3+2x^2/2 +C) x= 1}

Area = {(x^3+x^2+C) at x= 3} -{(x^3+x^2+C) at xx = 1}

Area = {2^3+2^2 +C}- {1^3+1^2+C}

Area = 12-2 +C-C.

Area = 10.

Therefore the area under the function 3x^2-2x   between x =2 and x = 1 is 10 sq units.

giorgiana1976's profile pic

giorgiana1976 | College Teacher | (Level 3) Valedictorian

Posted on

Since there is not established the other boundary curve, we'll suppose that we have to calculate the area between f(x), the lines x=1 and x=2 and the x axis.

The definite integral will be calculated with Leibniz-Newton formula:

Int f(x)dx = F(b)-F(a)

We'll calculate the indefinite integral of f(x):

Int f(x)dx = Int (3x^2 + 2x)dx

We'll use the property of integral to be additive:

 Int (3x^2 + 2x)dx = Int 3x^2dx + Int 2xdx

 Int 3x^2dx = 3*x^3/3 + C

Int 3x^2dx =x^3 + C

Int 2xdx = 2*x^2/2 + C

Int 2xdx = x^2 + C

 Int (3x^2 + 2x)dx = x^3 + x^2 + C

F(2) - F(1) = 2^3 + 2^2 - 1^3 - 1^2

F(2) - F(1) = 8 + 4 - 2

F(2) - F(1) = 10

The area bounded by the curve of f(x) and the lines x=1, x=2 and x axis is A=10.

william1941's profile pic

william1941 | College Teacher | (Level 3) Valedictorian

Posted on

We have the function. f(x) = 3x^2 + 2x.

To find the required area we need to find the definite integral of 3x^2 + 2x between x = 1 and x =2.

Now the integral of the term x^n is given as x^(n+1) / (n+1)

So Int [3x^2 + 2x]

=> 3*x^3/3 + 2x^2/2

=> x^3 + x^2

Between the limits x=1 and x=2

x^3 + x^2 = 2^3 + 2^2 - 1^3 - 1^2

=> 8 + 4 -1- 1

=> 12 - 2

=> 10

The required area is 10

We’ve answered 318,915 questions. We can answer yours, too.

Ask a question