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Level 5-6 Shapes - Angles
A 45 degree angle is known as an acute angle.

Level 5-6 Shapes - Angles

Master KS3 angle facts. Identify acute and obtuse angles, use straight-line and around-a-point rules, and solve missing-angle problems with clear reasoning.

Fascinating Fact:

Crossing roads create vertical opposite angles that are equal; if one angle is 46°, the opposite is also 46°.

In KS3 Maths, angle work focuses on key rules: angles on a straight line add to 180°, around a point to 360°, vertically opposite angles are equal, and angles in a triangle total 180°. You’ll apply these to find unknown angles, including where parallel lines are involved.

  • Acute angle: An angle smaller than 90°.
  • Vertically opposite angles: Equal angles formed when two straight lines cross.
  • Corresponding angles: Equal angles formed when a transversal crosses parallel lines; they sit in matching “corners.”
What are the essential KS3 angle facts I should remember?

Know these: straight line = 180°, around a point = 360°, triangle = 180°, vertically opposite angles are equal, and parallel-line angle pairs can be equal or supplementary.

How do I find a missing angle on a straight line?

Angles on a straight line add to 180°. Subtract the known angle from 180°. For example, if one angle is 112°, the other is 180° − 112° = 68°.

What are alternate and corresponding angles with parallel lines?

With parallel lines, alternate angles (Z-shape) are equal, and corresponding angles (F-shape) are equal. Co-interior angles (C-shape) add to 180°.

1 .
What is 'angle A' in the equilateral triangle below?
50o
60o
70o
80o
The angles in a triangle add up to 180o
2 .
The angle in the picture below is a(n) .......
acute angle
obtuse angle
reflex angle
right angle
Right angles are exactly 90o
3 .
What is 'angle A' in the diagram below?
80o
100o
120o
140o
The angles on a straight line add up to 180o
4 .
What is 'angle A' in the regular hexagon below?
80o
120o
180o
240o
Remember that all the angles in a regular hexagon are the same and all the lengths of the sides are the same
5 .
The angle in the picture below is a(n) .......
acute angle
obtuse angle
reflex angle
right angle
Reflex angles are between 180o and 360o
6 .
What is 'angle A' in the diagram below?
90o
180o
210o
270o
The angles in a circle add up to 360o
7 .
What is 'angle A' in the regular pentagon below?
80o
88o
92o
108o
All angles in a regular pentagon are the same. (The length of the sides are also the same)
8 .
The angle in the picture below is a(n) .......
acute angle
obtuse angle
reflex angle
right angle
Acute angles are less than 90o
9 .
What is 'angle A' in the diagram below?
55o
65o
75o
85o
90o + 195o + 75o = 360o
10 .
The angle in the picture below is a(n) .......
acute angle
obtuse angle
reflex angle
right angle
Obtuse angles are between 90o and 180o
You can find more about this topic by visiting BBC Bitesize - Angles

Author:  Frank Evans (Specialist 11 Plus Teacher and Tutor)

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