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Important Questions

Triangles

ICSE · Class 9 · Mathematics

Most important questions from Triangles for ICSE Class 9 Mathematics board exam 2026. MCQs, short answer, and long answer questions with marks.

40 questions30 flashcards5 concepts

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A labeled diagram showing the vertices, sides, and angles of a basic triangle ABC.
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40 Questions·
multiple choicemultiple correct

Sample Questions

1multiple correct

Which of the following are valid congruence criteria for triangles? (Select all that apply)

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SSS, SAS, ASA, RHS

Valid congruence criteria are: SSS (Side-Side-Side), SAS (Side-Angle-Side), ASA (Angle-Side-Angle), AAS (Angle-Angle-Side), and RHS (Right angle-Hypotenuse-Side). AAA only ensures similarity, not congruence. SSA is not a valid criterion as it can lead to ambiguous cases.

2multiple choice

The exterior angle of a triangle is 120°. If one of the interior opposite angles is 50°, find the other interior opposite angle:

Show answer

70°

By the exterior angle theorem, an exterior angle equals the sum of the two non-adjacent interior angles. So: Exterior angle = Sum of two opposite interior angles. 120° = 50° + other angle. Therefore, other angle = 120° - 50° = 70°.

3multiple correct

If triangle ABC ≅ triangle PQR, and AB = 5 cm, BC = 7 cm, which of the following must be true?

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PQ = 5 cm, QR = 7 cm, ∠A = ∠P, Area of ABC = Area of PQR

When triangles are congruent (ABC ≅ PQR), corresponding parts are equal: AB = PQ = 5 cm, BC = QR = 7 cm, ∠A = ∠P, ∠B = ∠Q (not ∠R), ∠C = ∠R. Congruent triangles have equal areas.

4multiple choice

A triangle can have at most how many obtuse angles?

Show answer

1

A triangle can have at most one obtuse angle. If a triangle had two obtuse angles, their sum would exceed 180° (since each obtuse angle > 90°), but the sum of all three angles in a triangle must be exactly 180°. Therefore, maximum one obtuse angle is possible.

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Frequently Asked Questions

What are the important topics in Triangles for ICSE Class 9 Mathematics?
Triangles 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 Triangles — ICSE Class 9 Mathematics?
Understand the core concepts first, then work through the 40 practice questions available for this chapter. Revise formulas and definitions regularly, and use flashcards for quick recall before the exam.
How many important questions are there in Triangles?
There are 40 practice questions available for Triangles. These cover multiple question types including MCQs, short answer, and long answer questions.

Sources & Official References

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

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