Limits Involving Trigonometric Functions
The trigonometric functions sine and cosine have four important limit properties:
You can use these properties to evaluate many limit problems involving the six basic trigonometric functions.
Example 1: Evaluate 
.
Substituting 0 for x, you find that cos x approaches 1 and sin x − 3 approaches −3; hence,
Example 2: Evaluate 
Because cot x = cos x/sin x, you find 
The numerator approaches 1 and the denominator approaches 0 through positive values because we are approaching 0 in the first quadrant; hence, the function increases without bound and 
and the function has a vertical asymptote at x = 0.
Example 3: Evaluate 
Multiplying the numerator and the denominator by 4 produces
Example 4: Evaluate 
.
Because sec x = 1/cos x, you find that
