To determine whether the given limits are correct, we need to analyze each one carefully. Let's break them down one by one, using mathematical principles and properties of limits.
Limit as x Approaches Infinity
First, let's consider the limit:
lim x → ∞ ( π − 2 tan − 1 x ) ln x = 0
As x approaches infinity, the term tan-1(x) approaches π/2. Therefore, we can rewrite the expression:
(π - 2 tan-1(x)) approaches (π - π) = 0.
Now, we have:
lim x → ∞ (0) ln x.
Since ln x approaches infinity as x approaches infinity, we have a form of 0 multiplied by infinity, which is indeterminate. To resolve this, we can rewrite it as:
lim x → ∞ (π - 2 tan-1(x)) ln x = lim x → ∞ ln x / (1 / (π - 2 tan-1(x))).
As x approaches infinity, the denominator approaches 0, and the numerator approaches infinity. This results in an overall limit of 0. Thus, this limit is indeed correct.
Limit as x Approaches Zero
Next, we evaluate:
lim x → 0 (cosec x) ln x = 1
As x approaches 0, cosec x (which is 1/sin x) approaches infinity because sin x approaches 0. The natural logarithm, ln x, approaches negative infinity. This gives us an indeterminate form of infinity times negative infinity.
To analyze this further, we can rewrite it as:
lim x → 0 (cosec x) ln x = lim x → 0 ln x / (sin x).
Using L'Hôpital's Rule, we differentiate the numerator and denominator:
- Derivative of ln x is 1/x.
- Derivative of sin x is cos x.
Applying L'Hôpital's Rule gives us:
lim x → 0 (1/x) / (cos x) = lim x → 0 (1 / (x cos x)).
As x approaches 0, this limit approaches infinity, not 1. Therefore, this limit is incorrect.
Final Limit Evaluation
Lastly, we check:
lim x → 0 (cot x) ln x = e
As x approaches 0, cot x (which is cos x/sin x) approaches infinity, while ln x approaches negative infinity, leading to another indeterminate form.
We can rewrite this limit as:
lim x → 0 (cot x) ln x = lim x → 0 ln x / (tan x).
Using L'Hôpital's Rule again:
- Derivative of ln x is 1/x.
- Derivative of tan x is sec2(x).
Applying L'Hôpital's Rule gives us:
lim x → 0 (1/x) / (sec2(x)) = lim x → 0 (cos2(x) / x).
As x approaches 0, this limit approaches 0, not e. Therefore, this limit is also incorrect.
Summary of Findings
In summary:
- The first limit is correct: lim x → ∞ ( π − 2 tan − 1 x ) ln x = 0.
- The second limit is incorrect: lim x → 0 ( cosec x ) ln x ≠ 1.
- The third limit is incorrect: lim x → 0 ( cot x ) ln x ≠ e.
Understanding these limits requires a solid grasp of the behavior of functions as they approach critical points, and applying L'Hôpital's Rule can often help resolve indeterminate forms effectively.