Difficulty: Medium
Correct Answer: tan^2 A sin^2 A
Explanation:
Introduction / Context:
This problem tests identity-based simplification with trigonometric squares. The expression tan^2 A - sin^2 A looks like a difference, but it can be factorized using the relationship between tan and sin through cos. Specifically, tan^2 A = sin^2 A / cos^2 A. Substituting that converts everything into sin and cos, after which a common factor sin^2 A can be taken out. Finally, the remaining bracket simplifies using 1 - cos^2 A = sin^2 A. The end result becomes a clean product form, which is a typical goal in simplification questions.
Given Data / Assumptions:
Concept / Approach:
Rewrite tan^2 A in terms of sin and cos:
tan^2 A = sin^2 A / cos^2 A.
Then:
x = (sin^2 A / cos^2 A) - sin^2 A.
Factor sin^2 A and simplify the bracket:
(1/cos^2 A) - 1 = (1 - cos^2 A)/cos^2 A = sin^2 A / cos^2 A = tan^2 A.
So x becomes sin^2 A * tan^2 A.
Step-by-Step Solution:
1) Start:
x = tan^2 A - sin^2 A
2) Replace tan^2 A with sin^2 A / cos^2 A:
x = (sin^2 A / cos^2 A) - sin^2 A
3) Factor out sin^2 A:
x = sin^2 A * (1/cos^2 A - 1)
4) Combine terms inside the bracket:
1/cos^2 A - 1 = (1 - cos^2 A)/cos^2 A
5) Use identity 1 - cos^2 A = sin^2 A:
(1 - cos^2 A)/cos^2 A = sin^2 A / cos^2 A
6) Recognize sin^2 A / cos^2 A = tan^2 A:
x = sin^2 A * tan^2 A
Verification / Alternative check:
Take A = 45°:
tan 45° = 1 and sin 45° = √2/2, so sin^2 45° = 1/2.
Original: tan^2 A - sin^2 A = 1 - 1/2 = 1/2.
Product form: tan^2 A sin^2 A = 1 * 1/2 = 1/2.
They match, confirming the identity simplification.
Why Other Options Are Wrong:
• tan A sin A is missing squares and will not match for general A.
• cot and cosec forms are reciprocals and do not represent the same difference.
• sin^2 A / tan^2 A equals sin^2 A * cot^2 A, which is different from tan^2 A * sin^2 A.
Common Pitfalls:
• Forgetting that tan^2 A involves cos^2 A in the denominator.
• Replacing 1 - cos^2 A incorrectly (it equals sin^2 A, not sin A).
• Cancelling terms across subtraction before factoring (not valid).
Final Answer:
tan^2 A sin^2 A
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