
3-2 (b) Integration by substitution
Point 4 of 12 — Lesson 1: Integration Techniques (Substitution and By Parts) and Definite IntegralsQuestion bank: 9 questions (9 with pictures)
04 3-2 (b) Integration by substitution
Idea
- Used for integrals of the form .
- If then , so
- Steps: choose ; find ; rewrite the whole integral in (including and ); integrate; return to .
- Choose so that the new integral is simpler and a standard one; if the first choice fails, try another.
✍️ Worked examples
Example 6: Find (a) (b) .
Solution:
- (a) Put , so .
- .
- .
- (b) Put , so .
- .
- .
When the integrand has an extra factor of
- Put equal to the inner expression and write in terms of too.
✍️ Worked examples
Example 7: Find (a) (b) .
Solution:
- (a) Put , so and .
- .
- .
- (b) Put , so and .
- .
- .
Example 8: Find (a) (b) .
Solution:
- (a) Put , so and .
- .
- .
- (b) Put , so .
- .
Example 9: Find (a) (b) .
Solution:
- (a) Put , so .
- .
- (b) Put , so .
- .
Two rules proved by substitution
- Put in : it becomes , so
- Put in : it becomes .
📝 Question bank for this point
9 questions linked to this point only, 9 of them with pictures.