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Complementary Angles

ICSE · Class 9 · Mathematics

Flashcards for Complementary Angles — ICSE Class 9 Mathematics. Quick Q&A cards covering key concepts, definitions, and formulas.

41 questions28 flashcards5 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
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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What are the important topics in Complementary Angles for ICSE Class 9 Mathematics?
Complementary Angles covers several key topics that are frequently asked in ICSE Class 9 board exams. Focus on the core concepts listed on this page and practise related questions to build confidence.
How to score full marks in Complementary Angles — ICSE Class 9 Mathematics?
Understand the core concepts first, then work through the 41 practice questions available for this chapter. Revise formulas and definitions regularly, and use flashcards for quick recall before the exam.
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There are 28 flashcards for Complementary Angles covering key definitions, formulas, and concepts. Use them daily for 10–15 minutes for best results.

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