Trig-substitutions → Trig Rule
The goal is to simplify expression by CONVERTING terms of
x
into simplified expression in terms ofθ
.
How to do this? We can identify some trigonometric patterns in the expression and apply the Pythagorean Theorem
.
▶ Cheatsheet on previous note: Basic Integral Rules
▶ Cheatsheet on previous note: Basic Differential Rules
▶ Cheatsheet on previous note: All trig identities
▶ Back to previous note on: U-substitution → Chain Rule
▶ Practice at Khan academy: Trigonometric substitution
Refer to Khan academy: Introduction to trigonometric substitution
Example
In this expression, we can easily identify there is a "pythagorean-like terms":
We can see
x
and2
as two sides of a triangle:Once we identify the pattern, we can easily get some information out of it in terms of
θ
:From the information
tan(θ)=x/2
we can get the relationship betweenx & θ
, which is:x=2tan(θ)
And now we can convert the original expression to be in terms of
θ
:
Example
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