### Home > CALC > Chapter 1 > Lesson 1.2.3 > Problem1-58

1-58.

Estimate $A(f(x)$, $-3 ≤ x ≤ 3$) for $f(x) = 2x^2 + 1$. .

1. Using left endpoint rectangles. The first two rectangles are shown.

Regarding the word ESTIMATE: You are not being asked to make a guess. You still need to compute. Of course, the area using rectangles is an approximation of the actual area under $f(x)$.

Sketch the remaining rectangle. Notice: The height of the LAST rectangle is evaluated at $x = 2$ (not $x=3$).

Each rectangle has a base of $1$ and a height of $f(x)$. Area $= 1(f(-3) + f(-2) + f(-1) + f(0) + f(1) + f(2)) =$_____________

2. Using right endpoint rectangles.

Notice: The height of the FIRST rectangle is evaluated at $x = -2$. The height of the LAST rectangle is evaluated at $x = 3$.

Each rectangle has a base of $1$ and a height of $f(x)$. Area $= 1( f(-2) + f(-1) + f(0) + f(1) + f(2) + f(3)) =$_____________

3. Using trapezoids. What do you notice? Does this always happen?

The trapezoidal sum is the AVERAGE of the left- and right-endpoint sums! Expain why this happens (algebraically and geometrically).

Use the eTool below to view the graphs.
Click the link at right for the full version of the eTool: Calc 1-58 HW eTool