# Math Help - Approximate the area under the graph of f(x) and above the x-axis using n rectangles.

1. ## Approximate the area under the graph of f(x) and above the x-axis using n rectangles.

Approximate the area under the graph of f(x) and above the x-axis using n rectangles.
f(x)=3x^2-2 from x=1 to x=5; n=4; use the right endpoints

2. Originally Posted by plstevens
Approximate the area under the graph of f(x) and above the x-axis using n rectangles.
f(x)=3x^2-2 from x=1 to x=5; n=4; use the right endpoints
Hello plstevens,

$\int_{a}^{b}f(x)dx \approx \sum_{n=1}^{4}f(x_n)\Delta x$

Where $\Delta x =\frac{b-a}{n}=\frac{5-1}{4}=1$ and

$x_n=a+n \Delta x =1+n\Delta x \mbox{ for } n=1,2,3,4$

Plugging into the above formula we get

$\int_{a}^{b}f(x)dx \approx \sum_{n=1}^{4}f(x_n)\Delta x=f(2)+f(3)+f(4)+f(5)$

It is all down hillfrom here.

Good luck