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Complementary Angles — Flashcards

ICSE · Class 9 · Mathematics

28 flashcards for Complementary Angles (ICSE Class 9 Mathematics) to test yourself on key terms and facts. Part of the ICSE Class 9 Mathematics syllabus.

41 questions28 flashcards18 formulas & key relations5 concepts

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An illustration showing two acute angles whose sum is 90 degrees, defining them as complementary angles. Examples like 30 and 60 degrees, and a general case with x and (90-x) degrees.
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28 Flashcards·
Complementary anglesComplement of an angleDefinition and conceptSine and cosine complementary identity
Card 1Complementary angles

Solve: 30° and 60° form what type of angle pair?

Answer

Step 1: Add the angles: 30° + 60° = 90°. Step 2: Two acute angles are complementary if their sum is 90°. Answer: 30° and 60° are complementary angles.

Card 2Complementary angles

Solve: 70° and 20° form what type of angle pair?

Answer

Step 1: Add the angles: 70° + 20° = 90°. Step 2: Since the sum is 90°, the angles are complementary. Answer: 70° and 20° are complementary angles.

Card 3Complement of an angle

Find the complement of 48°.

Answer

Step 1: Use the formula: complement of θ° = (90 − θ)°. Step 2: Substitute θ = 48°. Step 3: 90° − 48° = 42°. Answer: 42°…

Card 4Complement of an angle

Find the complement of 35°.

Answer

Step 1: Use complement of θ° = (90 − θ)°. Step 2: 90° − 35° = 55°. Answer: 55°…

Card 5Complement of an angle

If one acute angle is x°, what is its complement?

Answer

Step 1: A complementary pair adds to 90°. Step 2: Subtract x° from 90°. Answer: The complement is (90 − x)°.

Card 6Definition and concept

Why are 30° and 60° called complementary angles?

Answer

Step 1: Check the sum: 30° + 60° = 90°. Step 2: Complementary angles are acute angles whose sum is 90°. Answer: They are complementary because their sum is 90°.

Card 7Definition and concept

Why is the complement of θ° written as (90 − θ)°?

Answer

Step 1: Complementary angles must add to 90°. Step 2: If one angle is θ°, the other angle must complete the sum to 90°. Step 3: So the missing angle is 90° − θ°. Answer: The complement of θ° is (90 − …

Card 8Sine and cosine complementary identity

Use the complementary identity to simplify: cos(90° − 47°).

Answer

Step 1: Use cos(90° − θ) = sin θ. Step 2: Here θ = 47°. Step 3: cos(90° − 47°) = sin 47°. Answer: sin 47°…

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Frequently Asked Questions

What are the important topics in Complementary Angles for ICSE Class 9 Mathematics?
Key topics in Complementary Angles include Core idea of complementary angles, Sine and cosine complementary identities, Tangent and cotangent complementary identities, Secant and cosecant complementary identities. Study these first, then practise questions on each for Class 9 exams.
How many flashcards are available for Complementary Angles?
There are 28 flashcards for Complementary Angles covering key definitions, facts and ideas. A few sample cards are shown on this page.
How should I revise Complementary Angles for Class 9 exams?
Learn the core ideas first, then work through the 41 practice questions on Complementary Angles. Revise definitions regularly and use flashcards for quick recall before the exam.

Sources & Official References

Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.

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