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  1. AP Calculus
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What is the difference between evaluating ∫abf(x)dx\int_a^b f(x) dx∫ab​f(x)dx and ∫a∞f(x)dx\int_a^\infty f(x) dx∫a∞​f(x)dx?

Definite Integral: Direct evaluation using the Fundamental Theorem of Calculus. Improper Integral: Requires expressing as a limit and evaluating the limit.

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What is the difference between evaluating ∫abf(x)dx\int_a^b f(x) dx∫ab​f(x)dx and ∫a∞f(x)dx\int_a^\infty f(x) dx∫a∞​f(x)dx?

Definite Integral: Direct evaluation using the Fundamental Theorem of Calculus. Improper Integral: Requires expressing as a limit and evaluating the limit.

Compare and contrast the convergence tests for series and improper integrals.

Series: Ratio test, comparison test, etc. Improper Integrals: Direct evaluation via limits, comparison theorems (comparing to known convergent/divergent integrals).

What is the difference between a definite integral and an indefinite integral?

Definite Integral: Has upper and lower bounds, evaluates to a numerical value. Indefinite Integral: Does not have bounds, evaluates to a function + C.

Compare the methods for handling discontinuities within the interval of integration for proper and improper integrals.

Proper Integrals: Discontinuities typically lead to undefined integrals. Improper Integrals: Discontinuities are handled by splitting the integral and using limits.

What is the difference between convergence and divergence?

Convergence: The limit approaches a finite value. Divergence: The limit approaches infinity or does not exist.

Compare the use of u-substitution in proper and improper integrals.

Proper Integrals: u-substitution simplifies the integrand. Improper Integrals: u-substitution simplifies the integrand before taking the limit.

Compare the use of integration by parts in proper and improper integrals.

Proper Integrals: Integration by parts helps to solve the integral. Improper Integrals: Integration by parts helps to solve the integral before taking the limit.

Compare the use of partial fraction decomposition in proper and improper integrals.

Proper Integrals: Partial fraction decomposition helps to solve the integral. Improper Integrals: Partial fraction decomposition helps to solve the integral before taking the limit.

Compare the use of the Fundamental Theorem of Calculus in proper and improper integrals.

Proper Integrals: Fundamental Theorem of Calculus is used to solve the integral. Improper Integrals: Fundamental Theorem of Calculus is used to solve the integral before taking the limit.

What is the difference between the integral of 1x\frac{1}{x}x1​ and 1x2\frac{1}{x^2}x21​?

∫1xdx=ln∣x∣+C\int \frac{1}{x} dx = ln|x| + C∫x1​dx=ln∣x∣+C and ∫1x2dx=−1x+C\int \frac{1}{x^2} dx = -\frac{1}{x} + C∫x21​dx=−x1​+C

How do you evaluate ∫0∞e−xdx\int_0^\infty e^{-x} dx∫0∞​e−xdx?

  1. Express as a limit: lim⁡b→∞∫0be−xdx\lim_{b \to \infty} \int_0^b e^{-x} dxlimb→∞​∫0b​e−xdx. 2) Evaluate the integral: lim⁡b→∞[−e−x]0b=lim⁡b→∞(−e−b+e0)\lim_{b \to \infty} [-e^{-x}]_0^b = \lim_{b \to \infty} (-e^{-b} + e^0)limb→∞​[−e−x]0b​=limb→∞​(−e−b+e0). 3) Evaluate the limit: lim⁡b→∞(−e−b+1)=1\lim_{b \to \infty} (-e^{-b} + 1) = 1limb→∞​(−e−b+1)=1. 4) The integral converges to 1.

How do you evaluate ∫1∞1x2dx\int_1^\infty \frac{1}{x^2} dx∫1∞​x21​dx?

  1. Express as a limit: lim⁡b→∞∫1b1x2dx\lim_{b \to \infty} \int_1^b \frac{1}{x^2} dxlimb→∞​∫1b​x21​dx. 2) Evaluate the integral: lim⁡b→∞[−1x]1b=lim⁡b→∞(−1b+1)\lim_{b \to \infty} [-\frac{1}{x}]_1^b = \lim_{b \to \infty} (-\frac{1}{b} + 1)limb→∞​[−x1​]1b​=limb→∞​(−b1​+1). 3) Evaluate the limit: lim⁡b→∞(−1b+1)=1\lim_{b \to \infty} (-\frac{1}{b} + 1) = 1limb→∞​(−b1​+1)=1. 4) The integral converges to 1.

How do you evaluate ∫011xdx\int_0^1 \frac{1}{\sqrt{x}} dx∫01​x​1​dx?

  1. Express as a limit: lim⁡a→0+∫a11xdx\lim_{a \to 0^+} \int_a^1 \frac{1}{\sqrt{x}} dxlima→0+​∫a1​x​1​dx. 2) Evaluate the integral: lim⁡a→0+[2x]a1=lim⁡a→0+(2−2a)\lim_{a \to 0^+} [2\sqrt{x}]_a^1 = \lim_{a \to 0^+} (2 - 2\sqrt{a})lima→0+​[2x​]a1​=lima→0+​(2−2a​). 3) Evaluate the limit: lim⁡a→0+(2−2a)=2\lim_{a \to 0^+} (2 - 2\sqrt{a}) = 2lima→0+​(2−2a​)=2. 4) The integral converges to 2.

How do you evaluate ∫1∞1xdx\int_1^\infty \frac{1}{x} dx∫1∞​x1​dx?

  1. Express as a limit: lim⁡b→∞∫1b1xdx\lim_{b \to \infty} \int_1^b \frac{1}{x} dxlimb→∞​∫1b​x1​dx. 2) Evaluate the integral: lim⁡b→∞[ln⁡∣x∣]1b=lim⁡b→∞(ln⁡(b)−ln⁡(1))\lim_{b \to \infty} [\ln|x|]_1^b = \lim_{b \to \infty} (\ln(b) - \ln(1))limb→∞​[ln∣x∣]1b​=limb→∞​(ln(b)−ln(1)). 3) Evaluate the limit: lim⁡b→∞(ln⁡(b)−0)=∞\lim_{b \to \infty} (\ln(b) - 0) = \inftylimb→∞​(ln(b)−0)=∞. 4) The integral diverges.

How do you evaluate ∫−∞0xexdx\int_{-\infty}^0 xe^x dx∫−∞0​xexdx?

  1. Express as a limit: lim⁡a→−∞∫a0xexdx\lim_{a \to -\infty} \int_a^0 xe^x dxlima→−∞​∫a0​xexdx. 2) Integrate by parts: u=x,dv=exdxu=x, dv=e^x dxu=x,dv=exdx, so du=dx,v=exdu=dx, v=e^xdu=dx,v=ex. Then ∫xexdx=xex−∫exdx=xex−ex+C\int xe^x dx = xe^x - \int e^x dx = xe^x - e^x + C∫xexdx=xex−∫exdx=xex−ex+C. 3) Evaluate the integral: lim⁡a→−∞[xex−ex]a0=lim⁡a→−∞[(0−e0)−(aea−ea)]=lim⁡a→−∞[−1−aea+ea]\lim_{a \to -\infty} [xe^x - e^x]_a^0 = \lim_{a \to -\infty} [(0 - e^0) - (ae^a - e^a)] = \lim_{a \to -\infty} [-1 - ae^a + e^a]lima→−∞​[xex−ex]a0​=lima→−∞​[(0−e0)−(aea−ea)]=lima→−∞​[−1−aea+ea]. 4) Evaluate the limit: lim⁡a→−∞[−1−aea+ea]=−1−0+0=−1\lim_{a \to -\infty} [-1 - ae^a + e^a] = -1 - 0 + 0 = -1lima→−∞​[−1−aea+ea]=−1−0+0=−1. 5) The integral converges to -1.

How do you evaluate ∫−∞∞11+x2dx\int_{-\infty}^{\infty} \frac{1}{1+x^2} dx∫−∞∞​1+x21​dx?

  1. Split the integral: ∫−∞∞11+x2dx=∫−∞011+x2dx+∫0∞11+x2dx\int_{-\infty}^{\infty} \frac{1}{1+x^2} dx = \int_{-\infty}^{0} \frac{1}{1+x^2} dx + \int_{0}^{\infty} \frac{1}{1+x^2} dx∫−∞∞​1+x21​dx=∫−∞0​1+x21​dx+∫0∞​1+x21​dx. 2) Express as limits: lim⁡a→−∞∫a011+x2dx+lim⁡b→∞∫0b11+x2dx\lim_{a \to -\infty} \int_a^0 \frac{1}{1+x^2} dx + \lim_{b \to \infty} \int_0^b \frac{1}{1+x^2} dxlima→−∞​∫a0​1+x21​dx+limb→∞​∫0b​1+x21​dx. 3) Evaluate the integral: lim⁡a→−∞[arctan⁡(x)]a0+lim⁡b→∞[arctan⁡(x)]0b=lim⁡a→−∞[arctan⁡(0)−arctan⁡(a)]+lim⁡b→∞[arctan⁡(b)−arctan⁡(0)]\lim_{a \to -\infty} [\arctan(x)]_a^0 + \lim_{b \to \infty} [\arctan(x)]_0^b = \lim_{a \to -\infty} [\arctan(0) - \arctan(a)] + \lim_{b \to \infty} [\arctan(b) - \arctan(0)]lima→−∞​[arctan(x)]a0​+limb→∞​[arctan(x)]0b​=lima→−∞​[arctan(0)−arctan(a)]+limb→∞​[arctan(b)−arctan(0)]. 4) Evaluate the limits: [0−(−π2)]+[π2−0]=π2+π2=π[0 - (-\frac{\pi}{2})] + [\frac{\pi}{2} - 0] = \frac{\pi}{2} + \frac{\pi}{2} = \pi[0−(−2π​)]+[2π​−0]=2π​+2π​=π. 5) The integral converges to π\piπ.

How do you evaluate ∫2∞1x(x−1)dx\int_2^{\infty} \frac{1}{x(x-1)} dx∫2∞​x(x−1)1​dx?

  1. Express as a limit: lim⁡b→∞∫2b1x(x−1)dx\lim_{b \to \infty} \int_2^b \frac{1}{x(x-1)} dxlimb→∞​∫2b​x(x−1)1​dx. 2) Partial fraction decomposition: 1x(x−1)=Ax+Bx−1\frac{1}{x(x-1)} = \frac{A}{x} + \frac{B}{x-1}x(x−1)1​=xA​+x−1B​. Solving gives A=−1A = -1A=−1 and B=1B = 1B=1. So, 1x(x−1)=−1x+1x−1\frac{1}{x(x-1)} = \frac{-1}{x} + \frac{1}{x-1}x(x−1)1​=x−1​+x−11​. 3) Evaluate the integral: lim⁡b→∞∫2b(−1x+1x−1)dx=lim⁡b→∞[−ln⁡∣x∣+ln⁡∣x−1∣]2b=lim⁡b→∞[ln⁡∣x−1x∣]2b=lim⁡b→∞[ln⁡∣b−1b∣−ln⁡∣2−12∣]\lim_{b \to \infty} \int_2^b (\frac{-1}{x} + \frac{1}{x-1}) dx = \lim_{b \to \infty} [-\ln|x| + \ln|x-1|]_2^b = \lim_{b \to \infty} [\ln|\frac{x-1}{x}|]_2^b = \lim_{b \to \infty} [\ln|\frac{b-1}{b}| - \ln|\frac{2-1}{2}|]limb→∞​∫2b​(x−1​+x−11​)dx=limb→∞​[−ln∣x∣+ln∣x−1∣]2b​=limb→∞​[ln∣xx−1​∣]2b​=limb→∞​[ln∣bb−1​∣−ln∣22−1​∣]. 4) Evaluate the limit: lim⁡b→∞[ln⁡∣b−1b∣−ln⁡(12)]=ln⁡(1)−ln⁡(12)=0−(−ln⁡(2))=ln⁡(2)\lim_{b \to \infty} [\ln|\frac{b-1}{b}| - \ln(\frac{1}{2})] = \ln(1) - \ln(\frac{1}{2}) = 0 - (-\ln(2)) = \ln(2)limb→∞​[ln∣bb−1​∣−ln(21​)]=ln(1)−ln(21​)=0−(−ln(2))=ln(2). 5) The integral converges to ln⁡(2)\ln(2)ln(2).

How do you evaluate ∫0∞cos(x)dx\int_0^{\infty} cos(x) dx∫0∞​cos(x)dx?

  1. Express as a limit: lim⁡b→∞∫0bcos(x)dx\lim_{b \to \infty} \int_0^b cos(x) dxlimb→∞​∫0b​cos(x)dx. 2) Evaluate the integral: lim⁡b→∞[sin(x)]0b=lim⁡b→∞(sin(b)−sin(0))\lim_{b \to \infty} [sin(x)]_0^b = \lim_{b \to \infty} (sin(b) - sin(0))limb→∞​[sin(x)]0b​=limb→∞​(sin(b)−sin(0)). 3) Evaluate the limit: lim⁡b→∞(sin(b)−0)\lim_{b \to \infty} (sin(b) - 0)limb→∞​(sin(b)−0). Since sin(b)sin(b)sin(b) oscillates between -1 and 1 as b approaches infinity, the limit does not exist. 4) The integral diverges.

How do you evaluate ∫031x−2dx\int_0^{3} \frac{1}{x-2} dx∫03​x−21​dx?

  1. Split the integral at the discontinuity: ∫031x−2dx=∫021x−2dx+∫231x−2dx\int_0^{3} \frac{1}{x-2} dx = \int_0^{2} \frac{1}{x-2} dx + \int_2^{3} \frac{1}{x-2} dx∫03​x−21​dx=∫02​x−21​dx+∫23​x−21​dx. 2) Express as limits: lim⁡b→2−∫0b1x−2dx+lim⁡a→2+∫a31x−2dx\lim_{b \to 2^-} \int_0^b \frac{1}{x-2} dx + \lim_{a \to 2^+} \int_a^3 \frac{1}{x-2} dxlimb→2−​∫0b​x−21​dx+lima→2+​∫a3​x−21​dx. 3) Evaluate the integral: lim⁡b→2−[ln⁡∣x−2∣]0b+lim⁡a→2+[ln⁡∣x−2∣]a3=lim⁡b→2−[ln⁡∣b−2∣−ln⁡∣−2∣]+lim⁡a→2+[ln⁡∣3−2∣−ln⁡∣a−2∣]=lim⁡b→2−[ln⁡∣b−2∣−ln⁡(2)]+lim⁡a→2+[ln⁡(1)−ln⁡∣a−2∣]\lim_{b \to 2^-} [\ln|x-2|]_0^b + \lim_{a \to 2^+} [\ln|x-2|]_a^3 = \lim_{b \to 2^-} [\ln|b-2| - \ln|-2|] + \lim_{a \to 2^+} [\ln|3-2| - \ln|a-2|] = \lim_{b \to 2^-} [\ln|b-2| - \ln(2)] + \lim_{a \to 2^+} [\ln(1) - \ln|a-2|]limb→2−​[ln∣x−2∣]0b​+lima→2+​[ln∣x−2∣]a3​=limb→2−​[ln∣b−2∣−ln∣−2∣]+lima→2+​[ln∣3−2∣−ln∣a−2∣]=limb→2−​[ln∣b−2∣−ln(2)]+lima→2+​[ln(1)−ln∣a−2∣]. 4) Evaluate the limits: Since lim⁡b→2−ln⁡∣b−2∣=−∞\lim_{b \to 2^-} \ln|b-2| = -\inftylimb→2−​ln∣b−2∣=−∞ and lim⁡a→2+ln⁡∣a−2∣=−∞\lim_{a \to 2^+} \ln|a-2| = -\inftylima→2+​ln∣a−2∣=−∞, both integrals diverge. 5) The integral diverges.

How do you evaluate ∫0∞x(1+x2)2dx\int_0^{\infty} \frac{x}{(1+x^2)^2} dx∫0∞​(1+x2)2x​dx?

  1. Express as a limit: lim⁡b→∞∫0bx(1+x2)2dx\lim_{b \to \infty} \int_0^b \frac{x}{(1+x^2)^2} dxlimb→∞​∫0b​(1+x2)2x​dx. 2) Use u-substitution: Let u=1+x2u = 1+x^2u=1+x2, then du=2xdxdu = 2x dxdu=2xdx, so xdx=12dux dx = \frac{1}{2} duxdx=21​du. The integral becomes 12∫1u2du=12∫u−2du=12[−1u]+C=−12(1+x2)+C\frac{1}{2} \int \frac{1}{u^2} du = \frac{1}{2} \int u^{-2} du = \frac{1}{2} [-\frac{1}{u}] + C = -\frac{1}{2(1+x^2)} + C21​∫u21​du=21​∫u−2du=21​[−u1​]+C=−2(1+x2)1​+C. 3) Evaluate the integral: lim⁡b→∞[−12(1+x2)]0b=lim⁡b→∞[−12(1+b2)−(−12(1+02))]=lim⁡b→∞[−12(1+b2)+12]\lim_{b \to \infty} [-\frac{1}{2(1+x^2)}]_0^b = \lim_{b \to \infty} [-\frac{1}{2(1+b^2)} - (-\frac{1}{2(1+0^2)})] = \lim_{b \to \infty} [-\frac{1}{2(1+b^2)} + \frac{1}{2}]limb→∞​[−2(1+x2)1​]0b​=limb→∞​[−2(1+b2)1​−(−2(1+02)1​)]=limb→∞​[−2(1+b2)1​+21​]. 4) Evaluate the limit: lim⁡b→∞[−12(1+b2)+12]=0+12=12\lim_{b \to \infty} [-\frac{1}{2(1+b^2)} + \frac{1}{2}] = 0 + \frac{1}{2} = \frac{1}{2}limb→∞​[−2(1+b2)1​+21​]=0+21​=21​. 5) The integral converges to 12\frac{1}{2}21​.

Explain why limits are necessary when evaluating improper integrals.

Limits allow us to approach infinity without actually reaching it, enabling us to evaluate the integral's behavior.

Describe the process of splitting an improper integral with infinite bounds.

Choose an arbitrary point 'c' and split the integral into two: one from negative infinity to 'c' and another from 'c' to infinity. Evaluate each separately.

Explain how to identify if an integral is improper.

Check if one or both limits are infinite, or if the function has a discontinuity within the integration interval.

What is the significance of convergence in the context of improper integrals?

Convergence indicates that the area under the curve approaches a finite value, allowing for a meaningful result.

What is the significance of divergence in the context of improper integrals?

Divergence indicates that the area under the curve does not approach a finite value, meaning the integral does not have a finite result.

How does the Fundamental Theorem of Calculus apply to improper integrals?

It is used to evaluate the integral after expressing it as a limit, but before evaluating the limit itself.

Why is it important to identify discontinuities within the integration interval?

Discontinuities can make an integral improper, requiring special treatment using limits.

Explain the relationship between improper integrals and area under a curve.

Improper integrals can be used to find the area under a curve even when the curve extends to infinity or has discontinuities.

Describe the role of substitution in evaluating improper integrals.

Substitution can simplify the integrand, making it easier to evaluate the integral before taking the limit.

Explain the importance of absolute value when dealing with logarithms in improper integrals.

Absolute value ensures that the logarithm is defined for all values within the integration interval, especially when dealing with negative values.