CLEP Calculus · Lesson 11 of 15
CLEP Calculus

Lesson 11: Antiderivatives & Indefinite Integrals


What You'll Learn

Content

The antiderivative and + C

A function F is an antiderivative of f if F'(x) = f(x). Because the derivative of any constant is 0, if F is one antiderivative then F(x) + C is an antiderivative for every constant C, and these are the only ones. So antidifferentiation never returns a single function — it returns a whole one-parameter family. The indefinite integral names that family:

∫ f(x) dx = F(x) + C,   where F'(x) = f(x)

The dx marks the variable of integration; the + C is the constant of integration and belongs on every indefinite integral. On the CLEP exam, dropping it turns a right answer into a wrong one.

The basic rules

Each rule below is a differentiation rule read backward. Verify any of them by differentiating the right-hand side.

Integral Antiderivative
∫ k dx kx + C
∫ xⁿ dx (n ≠ −1) xⁿ⁺¹/(n+1) + C
∫ (1/x) dx ln|x| + C
∫ eˣ dx eˣ + C
∫ aˣ dx (a > 0, a ≠ 1) aˣ/ln a + C
∫ cos x dx sin x + C
∫ sin x dx −cos x + C
∫ sec²x dx tan x + C

Power rule: add one to the exponent, then divide by the new exponent. It works for negative and fractional exponents too, once you rewrite radicals and quotients as powers (√x = x^(1/2), 1/x³ = x⁻³).

The n = −1 special case. The power rule fails for ∫ x⁻¹ dx because adding one gives exponent 0 and you would divide by 0. That single case is patched by the logarithm: ∫ (1/x) dx = ln|x| + C. The absolute value matters — 1/x is defined for negative x, and d/dx[ln|x|] = 1/x on both sides of 0.

Linearity and rewriting first

Antidifferentiation is linear: constants pull out front, and sums integrate term by term. There is no product rule and no quotient rule for integrals — if you face a product or a quotient, you must rewrite it as a sum of power/trig/exponential terms first. Common moves: split a fraction over its denominator ((x³ − 4x + 1)/x² = x − 4·x⁻¹ + x⁻²), expand a product ((x² + 1)² = x⁴ + 2x² + 1), and write radicals as powers.

Worked: ∫ (√x − 5/x + eˣ) dx = (2/3)x^(3/2) − 5 ln|x| + eˣ + C. The middle term is the n = −1 trap — 5/x integrates to a logarithm, not a power.

Verify by differentiating

The most reliable check in integration: differentiate your answer. If you recover the integrand, you are right. Do this whenever you have the seconds.

Initial conditions and motion

A particular antiderivative is one member of the family, fixed by an initial condition F(a) = b: integrate to get F(x) + C, substitute the condition, solve for C. Antiderivatives also recover motion. Given acceleration a(t), integrate once (using v(0)) to get velocity, and again (using s(0)) to get position:

v(t) = ∫ a(t) dt     s(t) = ∫ v(t) dt

One initial condition is needed per integration. Because the integral of a rate gives accumulated change, if s(t) is position then s(b) = s(a) + ∫ₐᵇ v(t) dt.

Key Takeaways

Practice Questions

Question 1
∫ (√x − 5/x + eˣ) dx =
Question 2
∫ (6x² − 4/x³ + 2) dx =
Question 3
∫ (4 cos x − 3 sec²x + 2eˣ) dx =
Question 4
If f'(x) = 3x² + 2 and f(0) = 4, then f(x) =
Question 5
A particle has acceleration a(t) = 6t − 4 with v(0) = 2. Its velocity function is
Question 6
Which of the following is an antiderivative of f(x) = 1/x?
Question 7
∫ (x³ − 4x + 1)/x² dx =
Question 8
∫ (x² + 1)² dx =
Question 9
Two functions F and G are both antiderivatives of the same continuous function f on an interval. Which statement must be true?
Question 10
A particle moves with velocity v(t) = 3t² − 6t and position s(0) = 4. Then s(2) =
Question 11
∫ (2ˣ + 4 cos x) dx =
Question 12
∫ (1/x) dx =
Show answer key & explanations

Answer Key

1. C — Correct: √x = x^(1/2) integrates to (2/3)x^(3/2), −5/x to −5 ln|x|, to . A differentiated the √x term instead of integrating it. B inverted the exponent fraction (3/2 instead of 2/3). D dropped the + C. E applied the power rule to −5/x instead of using the n = −1 log rule. Fix: rewrite radicals as powers, and treat any lone 1/x term as a logarithm.

2. B — Correct: 6x² → 2x³, −4x⁻³ → −4·x⁻²/(−2) = +2/x², 2 → 2x. A dropped the sign flip when dividing by the new exponent −2. C differentiated the middle term. D failed to integrate the constant 2 (left it as 2 instead of 2x). E forgot to divide the first term by its new exponent. Fix: divide by the new exponent every term, and watch the sign a negative exponent introduces.

3. A — Correct: ∫4 cos x = 4 sin x, ∫−3 sec²x = −3 tan x, ∫2eˣ = 2eˣ. B put the wrong sign on the cosine term (∫cos = +sin). C used sec x instead of tan x (the antiderivative of sec²x is tan x). D dropped + C. E left 4 cos x unintegrated. Fix: ∫cos = sin, ∫sec²x = tan x; verify by differentiating.

4. B — Correct: f(x) = x³ + 2x + C, and f(0) = C = 4. A found the family but ignored the initial condition. C left C unsolved despite the given value. D differentiated. E mis-solved for C (used 2 instead of 4). Fix: an initial-condition problem demands a number for C — substitute and solve.

5. A — Correct: v(t) = ∫(6t − 4) dt = 3t² − 4t + C, and v(0) = C = 2. B ignored the initial condition. C left C unsolved. D differentiated the acceleration. E forgot to divide 6t by the new exponent 2. Fix: integrate acceleration, then use v(0) to fix the constant.

6. D — Correct: any function ln|x| + C is an antiderivative of 1/x; here C = −5. A and B are derivative-style guesses (d/dx[1/x²] ≠ 1/x). C is undefined — the power rule fails at n = −1. E has derivative , not 1/x. Fix: the antiderivative of 1/x is ln|x| plus any constant.

7. D — Correct: split first, (x³ − 4x + 1)/x² = x − 4·(1/x) + x⁻², giving x²/2 − 4 ln|x| − 1/x + C. A mis-integrated the x term. B put the wrong sign on the log term. C put the wrong sign on the −1/x term (∫x⁻² = −1/x). E integrated the 1/x term as a power instead of a log. Fix: split the fraction, then treat each piece by its own rule — the 1/x piece is a logarithm.

8. E — Correct: expand (x² + 1)² = x⁴ + 2x² + 1, then integrate to x⁵/5 + (2/3)x³ + x + C. A invented a "chain rule for integrals." B failed to divide by the new exponents. C differentiated. D dropped + C. Fix: there is no chain rule for integrals — expand the product first.

9. E — Correct: two antiderivatives of the same function differ by a constant, so F − G is constant. A and C are too strong — the constant need not be 0. B and D contradict the fact that both have derivative f. Fix: same derivative on an interval ⇒ the functions differ by a constant.

10. E — Correct: s(t) = ∫(3t² − 6t) dt = t³ − 3t² + C; s(0) = C = 4, so s(2) = 8 − 12 + 4 = 0. A is the displacement s(2) − s(0), not the position. B keeps only the constant. C is alone at t = 2. D is an arithmetic slip. Fix: find s(t) with its constant, then evaluate at the requested time.

11. C — Correct: ∫2ˣ = 2ˣ/ln 2 and ∫4 cos x = 4 sin x. A forgot the 1/ln 2. B multiplied by ln 2 (that is differentiation). D applied the power rule to a variable exponent. E put the wrong sign on the sine term. Fix: ∫aˣ dx = aˣ/ln a + C.

12. A — Correct: the n = −1 special case, ∫(1/x) dx = ln|x| + C. B drops the absolute value, which is needed for negative x. C differentiated. D shows the power rule failing (division by zero). E is unrelated. Fix: memorize ∫(1/x) dx = ln|x| + C, absolute value included.

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