Math Problem Statement

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Part 1

For the function given​ below, find a formula for the Riemann sum obtained by dividing the interval

​[0,3030​]

into n equal subintervals and using the​ right-hand endpoint for each

c Subscript kck.

Then take a limit of this sum as

n right arrow infinityn → ∞

to calculate the area under the curve over

​[0,3030​]. f(x)= 900-x^2

Solution

To solve this problem, we'll follow these steps:

  1. Divide the interval [0,30][0, 30] into nn equal subintervals.
  2. Find the formula for the Riemann sum using the right-hand endpoints.
  3. Take the limit of this sum as nn approaches infinity to find the area under the curve.

Step 1: Divide the Interval

We divide the interval [0,30][0, 30] into nn equal subintervals. The width of each subinterval, Δx\Delta x, is:

Δx=300n=30n\Delta x = \frac{30 - 0}{n} = \frac{30}{n}

Step 2: Right-Hand Endpoints

The right-hand endpoint of the kk-th subinterval is:

xk=0+kΔx=30knfork=1,2,,nx_k = 0 + k \Delta x = \frac{30k}{n} \quad \text{for} \quad k = 1, 2, \ldots, n

Step 3: Riemann Sum

The Riemann sum SnS_n using the right-hand endpoints is given by:

Sn=k=1nf(xk)ΔxS_n = \sum_{k=1}^{n} f(x_k) \Delta x

Substitute f(x)=900x2f(x) = 900 - x^2 and xk=30knx_k = \frac{30k}{n}:

Sn=k=1n(900(30kn)2)30nS_n = \sum_{k=1}^{n} \left(900 - \left(\frac{30k}{n}\right)^2\right) \cdot \frac{30}{n}

Simplify inside the summation:

Sn=k=1n(900900k2n2)30nS_n = \sum_{k=1}^{n} \left(900 - \frac{900k^2}{n^2}\right) \cdot \frac{30}{n}

Distribute 30n\frac{30}{n}:

Sn=k=1n(90030n900k2n230n)S_n = \sum_{k=1}^{n} \left( 900 \cdot \frac{30}{n} - \frac{900k^2}{n^2} \cdot \frac{30}{n} \right)

Sn=k=1n(27000n27000k2n3)S_n = \sum_{k=1}^{n} \left( \frac{27000}{n} - \frac{27000k^2}{n^3} \right)

Separate the sums:

Sn=27000nk=1n127000n3k=1nk2S_n = \frac{27000}{n} \sum_{k=1}^{n} 1 - \frac{27000}{n^3} \sum_{k=1}^{n} k^2

Step 4: Summation Formulas

Use the summation formulas:

k=1n1=n\sum_{k=1}^{n} 1 = n k=1nk2=n(n+1)(2n+1)6\sum_{k=1}^{n} k^2 = \frac{n(n+1)(2n+1)}{6}

Substitute these into the Riemann sum:

Sn=27000nn27000n3n(n+1)(2n+1)6S_n = \frac{27000}{n} \cdot n - \frac{27000}{n^3} \cdot \frac{n(n+1)(2n+1)}{6}

Simplify:

Sn=2700027000(n+1)(2n+1)6n2S_n = 27000 - \frac{27000(n+1)(2n+1)}{6n^2}

Step 5: Take the Limit as nn \to \infty

Evaluate the limit:

limnSn=limn(2700027000(n+1)(2n+1)6n2)\lim_{n \to \infty} S_n = \lim_{n \to \infty} \left( 27000 - \frac{27000(n+1)(2n+1)}{6n^2} \right)

Simplify the fraction:

limn(n+1)(2n+1)n2=limn2n2+3n+1n2=limn(2+3n+1n2)=2\lim_{n \to \infty} \frac{(n+1)(2n+1)}{n^2} = \lim_{n \to \infty} \frac{2n^2 + 3n + 1}{n^2} = \lim_{n \to \infty} \left( 2 + \frac{3}{n} + \frac{1}{n^2} \right) = 2

Thus:

limnSn=270002700026=270009000=18000\lim_{n \to \infty} S_n = 27000 - \frac{27000 \cdot 2}{6} = 27000 - 9000 = 18000

Therefore, the area under the curve f(x)=900x2f(x) = 900 - x^2 over the interval [0,30][0, 30] is 18000\boxed{18000}.

Would you like more details or have any questions?

Here are some additional questions you might find interesting:

  1. How do you find the area under a curve using the left-hand endpoint for the Riemann sum?
  2. Can you explain the difference between Riemann sums and the definite integral?
  3. How do you interpret the result of the definite integral in a real-world context?
  4. What are the properties of definite integrals that make them useful in calculus?
  5. How do you calculate the area between two curves using integration?

Tip: When calculating Riemann sums, be careful with the placement of indices and summation limits to ensure accuracy in the final result.

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Math Problem Analysis

Mathematical Concepts

Calculus
Riemann Sums
Limits

Formulas

Riemann sum formula
Limit definition in calculus

Theorems

Limit properties in calculus

Suitable Grade Level

Advanced High School / College