Consider the function f(x)= -(x-3)^2+4f(x)=(x3)2+4 how do you write an equation using a limit to determine the area enclosed by f(x) and the x-axis?

1 Answer
Aug 14, 2017

A = lim_(nrarroo)sum_(i=1)^n (-(i4/n-2)^2+4) 4/n

Explanation:

The curve intersects the x axis at f(x) =0

or x=1 and x=5.

Cut the interval [1,5] into n pieces each of length (5-1)/n = 4/n

The right endpoints of the subintervals are 1+(4i)/n.

We can approximate the area under the curve on the i^(th) interval using a rectangle of

base 4/n and

height f(1+(4i)/n) = -(1+(4i)/n-3)^2+4 = -(i4/n-2)^2+4.

We then sum the areas of the rectangles sum_(i=1)^n (-(i4/n-2)^2+4) 4/n.

Finally, we take a limit as the subintervals get shorter and shorter (go to 0). This is aso the limit as the number of rectangles increases without bound (nrarroo)

A = lim_(nrarroo)sum_(i=1)^n (-(i4/n-2)^2+4) 4/n