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Evaluate: tan 25° tan 65° – cot 25° cot 65° - Mathematics

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Question

Evaluate: 

tan 25° tan 65° – cot 25° cot 65°

Evaluate
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Solution

Given: tan 25° tan 65° – cot 25° cot 65°.

65° = 90° – 25°

So, tan 65° = cot 25° and cot 65° = tan 25°.

Therefore, tan 25° · tan 65°

= tan 25° · cot 25°

= 1

And cot 25° · cot 65°

= cot 25° · tan 25°

= 1

The expression = 1 – 1

= 0

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Chapter 18: Trigonometric Ratios of Some Standard Angles and Complementary Angles - Exercise 18C [Page 380]

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Nootan Mathematics [English] Class 9 ICSE
Chapter 18 Trigonometric Ratios of Some Standard Angles and Complementary Angles
Exercise 18C | Q 4. | Page 380
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