Dabour Hub EGEgyptian Curriculum 2026/2027
3-1 (b) Indefinite integrals of logarithmic functions

3-1 (b) Indefinite integrals of logarithmic functions

Point 2 of 12 — Lesson 1: Integration Techniques (Substitution and By Parts) and Definite IntegralsQuestion bank: 9 questions (9 with pictures)

02 3-1 (b) Indefinite integrals of logarithmic functions

Rules

  • Since ddxln⁡∣x∣=1x for x≠0: ∫1x dx=ln⁡∣x∣+c(x≠0)
  • If f is differentiable and f(x)≠0: ∫f′(x)f(x) dx=ln⁡∣f(x)∣+c
  • ∫tan⁡x dx=−ln⁡∣cos⁡x∣+c=ln⁡∣sec⁡x∣+c.
  • ∫cot⁡x dx=ln⁡∣sin⁡x∣+c.
✍️ Worked examples

Example 2: Find (a) ∫(3x2+5x)dx (b) ∫7xln⁡3 dx (c) ∫2x+3x2+3x−2 dx.

Solution:

  • (a) ∫3x2 dx+5∫1x dx=x3+5ln⁡∣x∣+c.
  • (b) 7ln⁡3∫1x dx=7ln⁡3ln⁡∣x∣+c.
  • (c) The derivative of the denominator x2+3x−2 is 2x+3, which is the numerator.
  • So the integral is ln⁡∣x2+3x−2∣+c.

Geometric and physical applications

  • If the slope of the tangent at any point (x,y) is g(x), then the curve is y=∫g(x) dx, and the point given on the curve fixes c.
  • If the rate of change dAdt is given, then A=∫dAdt dt, and the starting value fixes c.
✍️ Worked examples

Example 3: The slope of the tangent to a curve at any point is 3+2x, and the curve passes through (e, 3e+5). Find its equation.

Solution:

  • y=∫(3+2x)dx=3x+2ln⁡x+c (for x>0).
  • Substitute (e,3e+5): 3e+5=3e+2ln⁡e+c=3e+2+c.
  • So c=3.
  • The curve is y=3x+2ln⁡x+3.

📝 Question bank for this point

9 questions linked to this point only, 9 of them with pictures.