Estimating Area Under a Curve

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Questions and Answers

When approximating the area under a curve using rectangles, which method generally provides the most accurate estimate?

  • Left endpoint rule
  • They all provide the same accuracy.
  • Right endpoint rule
  • Midpoint rule (correct)

As the number of rectangles used in approximating the area under a curve increases, what happens to the accuracy of the approximation?

  • It increases (correct)
  • It decreases
  • It stays the same
  • It fluctuates randomly

If a function is increasing over an interval, which method will overestimate the area under the curve?

  • Left endpoint rule
  • Midpoint rule
  • Right endpoint rule (correct)
  • All of the above

Consider a curve $y = f(x)$ on the interval $[a, b]$. If $\Delta x = \frac{b-a}{n}$, what does $n$ represent in the context of Riemann sums?

<p>The number of rectangles used. (A)</p> Signup and view all the answers

When using the left endpoint rule to approximate the area under a curve, what value determines the height of each rectangle?

<p>The function's value at the left endpoint of the subinterval. (C)</p> Signup and view all the answers

What is the primary difference between using the midpoint rule and the trapezoidal rule for approximating the area under a curve?

<p>The midpoint rule uses rectangles, while the trapezoidal rule uses trapezoids. (D)</p> Signup and view all the answers

Suppose you are approximating the area under a curve using rectangles of equal width. If you double the number of rectangles, what is the effect on the width of each individual rectangle?

<p>The width is halved. (C)</p> Signup and view all the answers

Under what condition would both the left and right endpoint rules give the exact same approximation for the area under a curve?

<p>When the function is constant. (A)</p> Signup and view all the answers

How does increasing the number of rectangles affect the difference between the approximations obtained by the left and right endpoint rules?

<p>The difference decreases. (C)</p> Signup and view all the answers

What is a definite integral's relationship to approximating the area using rectangles?

<p>The definite integral is the exact value of the area under a curve, which can be approximated using rectangles. (C)</p> Signup and view all the answers

Flashcards

Area Approximation

Estimating the area under a curve within an interval by dividing the area into rectangles and summing their areas.

Left Endpoint Rule

Using the left endpoint of each subinterval to determine the height of the rectangle.

Midpoint Rule

Using the midpoint of each subinterval to determine the height of the rectangle.

Right Endpoint Rule

Using the right endpoint of each subinterval to determine the height of the rectangle.

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Study Notes

  • It is possible to estimate the area under a curve on a given interval using rectangles.
  • To approximate the area under a curve on a given interval using n rectangles, use left endpoint, midpoint, and right endpoint evaluation rules.

Approximating Area with 16 Rectangles and endpoints for y = x² + 1 on [0, 1]

  • There are 16 rectangles, with evaluation points given by cᵢ = iΔx, where i ranges from 0 to 15.
  • A₁₆ = Δx Σ f(cᵢ) where i ranges from 0 to 15
    • The left endpoint approximation is ≈ 1.3027, which gives an underestimation of the area.
  • The midpoint approximation is ≈ 1.3330.
  • There are 16 rectangles, with evaluation points given by cᵢ = iΔx + Δx/2 where i ranges from 0 to 15.
  • A₁₆ = Δx Σ f(cᵢ) where i ranges from 0 to 15
    • The right endpoint approximation is ≈ 1.3652, which gives an overestimation of the area.
  • There are 16 rectangles, with evaluation points given by cᵢ = iΔx + Δx where i ranges from 0 to 15.
  • A = 4/3 ≈ 1.33333333 is the exact area.
  • A₁₆ = Δx Σ f(cᵢ) where i ranges from 0 to 15

Approximating Area with 16 Rectangles and endpoints for y = x² + 1 on [0, 2]

  • There are 16 rectangles, with evaluation points given by cᵢ = iΔx, where i ranges from 0 to 15.
  • A₁₆ = Δx Σ f(cᵢ) where i ranges from 0 to 15 ≈ 4.4219
  • There are 16 rectangles, with evaluation points given by cᵢ = iΔx + Δx/2 where i ranges from 0 to 15.
  • There are 16 rectangles, with evaluation points given by cᵢ = iΔx + Δx where i ranges from 0 to 15.
  • A₁₆ = Δx Σ f(cᵢ) where i ranges from 0 to 15 ≈ 4.6640
  • A₁₆ = Δx Σ f(cᵢ) where i ranges from 0 to 15 ≈ 4.9219

Approximating Area with 16 Rectangles and endpoints for y = √x + 2 on [1, 4]

  • There are 16 rectangles, with evaluation points given by cᵢ = 1 + iΔx, where i ranges from 0 to 15.
  • A₁₆ = Δx Σ f(cᵢ) where i ranges from 0 to 15 ≈ 6.2663
  • There are 16 rectangles, with evaluation points that are midpoints given by cᵢ = 1 + iΔx + Δx/2 where i ranges from 0 to 15.
  • A₁₆ = Δx Σ f(cᵢ) where i ranges from 0 to 15 ≈ 6.3340
  • There are 16 rectangles, with evaluation points that are the right endpoints given by cᵢ = 1 + iΔx, where i ranges from 1 to 16.
  • A₁₆ = Δx Σ f(cᵢ) where i ranges from 1 to 16 ≈ 6.4009

Approximating Area with 16 Rectangles and endpoints for y = e⁻²ˣ on [-1, 1]

  • There are 16 rectangles, with evaluation points as the left endpoints given by cᵢ = -1 + iΔx - Δx where i ranges from 1 to 16.
  • A₁₆ = Δx Σ f(cᵢ) where i ranges from 1 to 16 ≈ 4.0991
  • There are 16 rectangles, with evaluation points as the midpoints given by cᵢ = -1 + iΔx - Δx/2 where i ranges from 1 to 16.
  • A₁₆ = Δx Σ f(cᵢ) where i ranges from 1 to 16 ≈ 3.6174
  • There are 16 rectangles, with evaluation points as the right endpoints given by cᵢ = -1 + iΔx where i ranges from 1 to 16.
  • A₁₆ = Δx Σ f(cᵢ) where i ranges from 1 to 16 ≈ 3.1924

Approximating Area with 50 Rectangles and endpoints for y = cos x on [0, π/2]

  • There are 50 rectangles, with evaluation points given by cᵢ = iΔx where i is from 0 to 49.
  • A₅₀ = Δx Σ f(cᵢ) where i ranges from 0 to 49 ≈ 1.0156
  • There are 50 rectangles, with evaluation points given by cᵢ = Δx/2 + iΔx where i is from 0 to 49.
  • A₅₀ = Δx Σ f(cᵢ) where i ranges from 0 to 50 ≈ 1.00004
  • There are 50 rectangles, with evaluation points given by cᵢ = Δx + iΔx where i is from 0 to 49.
  • A₅₀ = Δx Σ f(cᵢ) where i ranges from 0 to 49 ≈ 0.9842

Approximating Area with 100 Rectangles and endpoints for y = x³ - 1 on [-1, 1]

  • There are 100 rectangles and the evaluation points are left endpoints which are given by cᵢ = -1 + iΔx – Δx where i is from 1 to 100.
  • A₁₀₀ = Δx Σ f(cᵢ) where i ranges from 1 to 100 ≈ -2.02
  • There are 100 rectangles and the evaluation points are midpoints which are given by cᵢ = -1 + iΔx Δx/2 where i is from 1 to 100.
  • A₁₀₀ = Δx Σ f(cᵢ) ≈ -2 where i ranges from 1 to 100
  • There are 100 rectangles and the evaluation points are right endpoints which are given by cᵢ = -1 + iΔx where i is from 1 to 100.
  • A₁₀₀ = Δx Σ f(cᵢ) where i ranges from 1 to 100 ≈ -1.98

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