Vidaara.orgClass 9 · Mathematics
CodeVID-M09-06-ASP-01
Angle Sum Property of a Triangle — Assignment
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
- Show all working for Sections B, C and D. Only final answers are given at the end — for full solutions, raise your doubts with your teacher.
Section A — Multiple Choice Questions
5 × 1 = 5 marks
1.
The angles of a triangle sum to:
- A.$90^\circ$
- B.$180^\circ$
- C.$270^\circ$
- D.$360^\circ$
2.
An exterior angle equals the sum of the two:
- A.adjacent angles
- B.interior opposite angles
- C.right angles
- D.base angles
3.
A triangle can have at most one:
- A.acute angle
- B.right or obtuse angle
- C.side
- D.vertex
4.
Each angle of an equilateral triangle is:
- A.$45^\circ$
- B.$60^\circ$
- C.$90^\circ$
- D.$30^\circ$
5.
If two angles are $50^\circ$ and $60^\circ$, the third is:
- A.$60^\circ$
- B.$70^\circ$
- C.$80^\circ$
- D.$90^\circ$
Section B — Short Answer (2 marks)
4 × 2 = 8 marks
6.
Two angles of a triangle are $40^\circ$ and $75^\circ$. Find the third.
7.
An exterior angle is $120^\circ$. What do the two interior opposite angles sum to?
8.
Find each angle of an equilateral triangle.
9.
Can a triangle have two right angles?
Section C — Short Answer (3 marks)
4 × 3 = 12 marks
10.
The angles of a triangle are in ratio $2:3:4$. Find them.
11.
One angle is $90^\circ$ and another $35^\circ$. Find the third.
12.
An exterior angle is $110^\circ$ and one interior opposite angle is $45^\circ$. Find the other.
13.
The angles are $x,\ x+10,\ x+20$. Find them.
Section D — Long Answer (5 marks)
2 × 5 = 10 marks
14.
The angles of a triangle are $(2x)^\circ,(3x)^\circ,(4x)^\circ$. Find each.
15.
An exterior angle of a triangle is $135^\circ$ and the interior opposite angles are equal. Find each interior opposite angle and all three interior angles.
Answer Key
Section A — Multiple Choice Questions
- (B) $180^\circ$
- (B) interior opposite angles
- (B) right or obtuse angle
- (B) $60^\circ$
- (B) $70^\circ$
Section B — Short Answer (2 marks)
- $65^\circ$.
- $120^\circ$.
- $60^\circ$.
- No.
Section C — Short Answer (3 marks)
- $40^\circ,60^\circ,80^\circ$.
- $55^\circ$.
- $65^\circ$.
- $50^\circ,60^\circ,70^\circ$.
Section D — Long Answer (5 marks)
- $40^\circ,60^\circ,80^\circ$.
- Each interior opposite $=67.5^\circ$; interior angles $67.5^\circ,67.5^\circ,45^\circ$.
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