Riemann Sums 070216
1. The problem asks to calculate three types of Riemann sums for the function $g(x)$ on given intervals:
A. Right Riemann sum $R_4$ on $[0,2]$
B. Left Riemann sum $L_3$ on $[1,4]$
C. Midpoint Riemann sum $M_3$ on $[0.5,3.5]$
2. The formulas for Riemann sums are:
- Right sum: $$R_n = \sum_{i=1}^n f(x_i) \Delta x$$ where $x_i$ are the right endpoints.
- Left sum: $$L_n = \sum_{i=0}^{n-1} f(x_i) \Delta x$$ where $x_i$ are the left endpoints.
- Midpoint sum: $$M_n = \sum_{i=0}^{n-1} f\left(\frac{x_i + x_{i+1}}{2}\right) \Delta x$$ where midpoints are used.
3. We need to find $\Delta x$ and the sample points for each sum.
A. For $R_4$ on $[0,2]$:
- $\Delta x = \frac{2-0}{4} = 0.5$
- Right endpoints: $x_1=0.5$, $x_2=1.0$, $x_3=1.5$, $x_4=2.0$
- Using the graph description, approximate $g(0.5)$, $g(1.0)$, $g(1.5)$, $g(2.0)$:
- $g(0.5) \approx 0.5$
- $g(1.0) \approx 1.2$
- $g(1.5) \approx 1.8$
- $g(2.0) \approx 2.1$
- Calculate:
$$R_4 = 0.5 \times (0.5 + 1.2 + 1.8 + 2.1) = 0.5 \times 5.6 = 2.8$$
B. For $L_3$ on $[1,4]$:
- $\Delta x = \frac{4-1}{3} = 1$
- Left endpoints: $x_0=1$, $x_1=2$, $x_2=3$
- Approximate $g(1)$, $g(2)$, $g(3)$:
- $g(1) \approx 1.2$
- $g(2) \approx 2.1$
- $g(3) \approx 1.8$
- Calculate:
$$L_3 = 1 \times (1.2 + 2.1 + 1.8) = 5.1$$
C. For $M_3$ on $[0.5,3.5]$:
- $\Delta x = \frac{3.5-0.5}{3} = 1$
- Subintervals: $[0.5,1.5]$, $[1.5,2.5]$, $[2.5,3.5]$
- Midpoints:
- $1.0$, $2.0$, $3.0$
- Approximate $g(1.0)$, $g(2.0)$, $g(3.0)$:
- $g(1.0) \approx 1.2$
- $g(2.0) \approx 2.1$
- $g(3.0) \approx 1.8$
- Calculate:
$$M_3 = 1 \times (1.2 + 2.1 + 1.8) = 5.1$$
4. Final answers:
- $R_4 = 2.8$
- $L_3 = 5.1$
- $M_3 = 5.1$