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Let 
f be the function defined by 
f(x)=(2)/(x). If three subintervals of equal length are used, what is the value of the trapezoidal sum approximation for 
int_(3)^(9)(2)/(x)dx ? Round to the nearest thousandth if necessary.
Answer:

Let f f be the function defined by f(x)=2x f(x)=\frac{2}{x} . If three subintervals of equal length are used, what is the value of the trapezoidal sum approximation for 392xdx \int_{3}^{9} \frac{2}{x} d x ? Round to the nearest thousandth if necessary.\newlineAnswer:

Full solution

Q. Let f f be the function defined by f(x)=2x f(x)=\frac{2}{x} . If three subintervals of equal length are used, what is the value of the trapezoidal sum approximation for 392xdx \int_{3}^{9} \frac{2}{x} d x ? Round to the nearest thousandth if necessary.\newlineAnswer:
  1. Calculate Subinterval Width: To approximate the integral of f(x)=2xf(x) = \frac{2}{x} from x=3x = 3 to x=9x = 9 using the trapezoidal rule with three subintervals, we first need to calculate the width of each subinterval. The total interval length is 93=69 - 3 = 6. Since we are using three subintervals, the width (hh) of each subinterval is 63=2\frac{6}{3} = 2.
  2. Evaluate Function at Endpoints: Next, we need to evaluate the function f(x)f(x) at the endpoints of the subintervals. The endpoints are x=3x = 3, x=5x = 5, x=7x = 7, and x=9x = 9. We calculate f(3)f(3), f(5)f(5), f(7)f(7), and f(9)f(9).\newlinef(3)=23f(3) = \frac{2}{3}\newlinex=3x = 300\newlinex=3x = 311\newlinex=3x = 322
  3. Apply Trapezoidal Rule: Now we apply the trapezoidal rule, which is given by the formula:\newlineTrapezoidal sum =h2[f(x0)+2f(x1)+2f(x2)++2f(xn1)+f(xn)]= \frac{h}{2} \cdot [f(x_0) + 2\cdot f(x_1) + 2\cdot f(x_2) + \ldots + 2\cdot f(x_{n-1}) + f(x_n)]\newlinewhere hh is the width of each subinterval, x0x_0 to xnx_n are the endpoints of the subintervals, and nn is the number of subintervals.
  4. Perform Addition: Plugging in the values we have:\newlineTrapezoidal sum=22×[f(3)+2f(5)+2f(7)+f(9)]Trapezoidal\ sum = \frac{2}{2} \times [f(3) + 2\cdot f(5) + 2\cdot f(7) + f(9)]\newline=1×[(23)+2(25)+2(27)+(29)]= 1 \times [\left(\frac{2}{3}\right) + 2\cdot\left(\frac{2}{5}\right) + 2\cdot\left(\frac{2}{7}\right) + \left(\frac{2}{9}\right)]\newline=(23)+(45)+(47)+(29)= \left(\frac{2}{3}\right) + \left(\frac{4}{5}\right) + \left(\frac{4}{7}\right) + \left(\frac{2}{9}\right)
  5. Convert to Common Denominator: We now perform the addition:\newline=23+45+47+29= \frac{2}{3} + \frac{4}{5} + \frac{4}{7} + \frac{2}{9}\newlineTo add these fractions, we need a common denominator, which is the least common multiple of 33, 55, 77, and 99. The LCM of these numbers is 315315.\newlineSo we convert each fraction to have the denominator of 315315:\newline=23105105+456363+474545+293535= \frac{2}{3}\cdot\frac{105}{105} + \frac{4}{5}\cdot\frac{63}{63} + \frac{4}{7}\cdot\frac{45}{45} + \frac{2}{9}\cdot\frac{35}{35}\newline=210315+252315+180315+70315= \frac{210}{315} + \frac{252}{315} + \frac{180}{315} + \frac{70}{315}
  6. Add Fractions: Adding the fractions together, we get:\newline= (210+252+180+70)/315(210 + 252 + 180 + 70) / 315\newline= 712/315712 / 315\newlineNow we simplify the fraction if possible and round to the nearest thousandth.\newline712/3152.260712 / 315 \approx 2.260

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