# Math Help - is this a "geometric formula" or calculus usage?

1. ## is this a "geometric formula" or calculus usage?

use a geometric formula to evaluate the integral

integral from 0 to 3

$(2x+1)dx$

I integrated the problem, getting $x^2 + x$

Then I used the fundamental theorem of calculus, and I got 12-0 = 12..

Did I use a geometric formula or just calculus?? If I used Calculus, how do I find the answer via geometric formula??

2. Originally Posted by elpermic
use a geometric formula to evaluate the integral

integral from 0 to 3

$(2x+1)dx$

I integrated the problem, getting $x^2 + x$

Then I used the fundamental theorem of calculus, and I got 12-0 = 12..

Did I use a geometric formula or just calculus?? If I used Calculus, how do I find the answer via geometric formula??
The function $f(x)=2x+1$ on the interval $[0,3]$ forms a triangle. Use that.

3. Ok, I did that.. Got $A = {{1/2}}(3)(7) = {{21/2}}$

What am I doing wrong??

4. Originally Posted by elpermic
Ok, I did that.. Got $A = {{1/2}}(3)(7) = {{21/2}}$

What am I doing wrong??
$f(0)\ne{0}$

5. I got it now..

From [0, 3] it isn't a triangle, it's a trapezoid.