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Definite integralsCalculusCollegeabout 0:57

Definite integral of 1/sqrt(x) from 1 to 4: animated lesson

A narrated, step-by-step definite integrals video lesson with captions. Final answer: 2.

Video with a synthetic English voice and captions. Pick another language for subtitles in that language, or open the interactive version.

Video narrated by a synthetic voice (Piper TTS, en_US-ljspeech-high voice (LJ Speech dataset, public domain)); the steps come from our maths engine and the answer was checked independently. Download MP4 (0.4 MB) · Captions (WebVTT)

Steps on screen

  1. 1. The problem
    Evaluating an integral
    ∫141x dx\int_{1}^{4} \frac{1}{\sqrt{x}}\,dx
  2. 2. Steps, part 1
    1. ∫141x dx\int_{1}^{4} \frac{1}{\sqrt{x}}\,dx
      Start with the definite integral
    2. ∫x−12 dx=2x12\int {x}^{\frac{-1}{2}}\,dx = 2{x}^{\frac{1}{2}}
      Power rule: ∫ xⁿ dx = xⁿ⁺¹/(n+1)
    3. ∫1x−12 dx=2x12\int 1{x}^{\frac{-1}{2}}\,dx = 2{x}^{\frac{1}{2}}
      Constant multiple rule: ∫ k·f dx = k∫ f dx
    4. F(x)=2x12F(x) = 2{x}^{\frac{1}{2}}
      Antiderivative
  3. 3. Steps, part 2
    1. F(4)−F(1)=4−2=2F(4) - F(1) = 4 - 2 = 2
      Apply the fundamental theorem of calculus
  4. 4. The answer
    ∫141x dx=2\int_{1}^{4} \frac{1}{\sqrt{x}}\,dx = 2

    ∫ from 1 to 4 = 2

  5. 5. Check
    • Differentiated the antiderivative and compared it with the integrand ✓
    • Adaptive Simpson's rule gives 2 ✓

Transcript

The problem. Here is the problem: integral of 1/sqrt(x) from 1 to 4. Evaluate the definite integral of 1 / sqrt(x) from x equals 1 to x equals 4.

Steps, part 1. Start with the definite integral. Power rule: the integral of x to the power n dx equals x to the power n plus 1/(n plus 1). Constant multiple rule: the integral of k times f dx equals k the integral of f dx. Antiderivative.

Steps, part 2. Apply the fundamental theorem of calculus.

The answer. So the answer is 2. A definite integral gives the signed area between the curve and the x-axis: area above the axis counts as positive and area below counts as negative.

Check. Differentiated the antiderivative and compared it with the integrand, which checks out. Adaptive Simpson prime s rule gives 2, which checks out.

About definite integrals

Evaluate definite integrals with the fundamental theorem of calculus.

Definite integral of 1/sqrt(x) from 1 to 4: Animated Lesson