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5 questions · self-marked practice — reveal the answer and mark yourself.

Question 12 Marks
Two adjacent angles are equal. Is it necessary that each of these angles will be a right angle? Justify your answer.
Answer
No, each of these angles will be a right angle only they form a linear pair, i.e., when the non-common arms of the given two adjacent angles are two opposite rays & common arm is perpendicular to them.
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Question 22 Marks
Can a triangle have all angles less than $60^\circ ?$ Give reason for your answer.
Answer
A triangle cannot have all angles less than $60^{\circ}$. Then, sum of all the angles will be less than $180^{\circ}$ whereas sum of all the angles of a triangle is always $180^{\circ}$.
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Question 32 Marks
Can a triangle have two obtuse angles? Give reason for your answer.
Answer
An angle whose measure is more than $90^{\circ}$ but less than $180^{\circ}$ is called an obtuse angle. A triangle cannot have two obtuse angles because the sum of all the angles of it cannot be more than $180^{\circ}$. It is always equal to $180^{\circ}$.
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Question 42 Marks
If one of the angles formed by two intersecting lines is a right angle, what can you say about the other three angles? Give reason for your answer.
Answer
If two intersect each other at a point, then four angles are formed. If one of these four angles is a right angle, then each of the other three angles will also be a right by linear pair axiom.
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Question 52 Marks
How many triangles can be drawn having its angles as $53^{\circ}, 64^{\circ}$ and $63^{\circ}$ ? Give reason for your answer.
Answer
Infinitely many triangles,
The sum of given angles $=53^{\circ}+64^{\circ}+63^{\circ}=180^{\circ}$
Here, we see that sum of all interior angles of triangle is $180^{\circ}$, so infinitely many triangles can be drawn.
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2 Marks Questions - Maths STD 9 Questions - Vidyadip