Angles

Types of Angles

Two rays meeting at a vertex form an angle. Measure in degrees (°).

Every triangle's angles add to 180°. If two angles are 60° and 70°, the third = 180 − 130 = 50°.

Indian context: The tip of a dosa on a tawa often forms an acute angle; a fully opened folded newspaper makes a straight angle.

NCERT anchor: Math-Magic 4, Ch 4 — Tick-Tick-Tick (clock angles); Ch 11 — Fields and Fences

Classify 85°, 90°, 110°, 180°

Step 1 — 85° < 90° → **acute**.
Step 2 — 90° → **right**.
Step 3 — 110° between 90° and 180° → **obtuse**.
Step 4 — 180° → **straight**.

At 3 o'clock, what angle do clock hands make?

Step 1 — Hour hand at 3, minute hand at 12.
Step 2 — Quarter turn of a circle = 90°.
Answer: **90° (right angle)**

Mistake	Why it happens	Fix
Bigger angle always means longer rays	Judging by ray length drawn	Angle size is turn, not line length
All triangle angles can be obtuse	Drawing without checking sum	At most one obtuse angle in a triangle
6 o'clock is a right angle	Confusing 3 and 6 on clock	6:00 → 180° straight, not 90°
0° is an acute angle	Including zero in acute	Acute means greater than 0° and less than 90°

Classify 45°, 95°, 180°.
Clock angle at 9:00?
Two angles of a triangle are 50° and 60°. Third angle?
Stretch: Can a triangle have angles 80°, 60°, and 50°? Add them to check. (yes — sum 180°)

Revision tip: Use your book corner as a 90° checker — compare unknown angles to it: smaller = acute, larger = obtuse.

Open the Practice tab for graded questions on Types of Angles.