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← Back to Geometry
1Lines, Rays, Segments2Types of Angles3Triangles by Sides4Triangles by Angles5Quadrilaterals63D Solids7Parts of a Circle8Line Symmetry9Rotational Symmetry

Concept 1 of 9

Lines, Rays, Segments

1

Today's big idea

Endpoints name the mark: 2 make a segment, 1 makes a ray, none makes a full line.

Parallel = never meet. Perpendicular = meet at 90°.

2

How it works

👀 What's going on?

You have drawn hundreds of straight marks on paper. Geometry gives each kind of mark its own name. Mix two names up and a whole answer can go wrong.

💡 Here's the trick

Line · Ray · SegmentLINEextends forever in BOTH directionsRAYstarts at a point · one directionSEGMENTtwo endpoints · fixed lengthParallel ‖ never meet · Perpendicular ⊥ meet at 90°

Look at the diagram above. A point is an exact spot with no size at all. A line runs on for ever in both directions. A ray starts at one spot and runs on one way only. A line segment stops at both ends, so it has a length you can measure. Two lines can also be parallel, intersecting or perpendicular.

🪄 How to do it

  1. 1.Count the stopping ends of the mark in the diagram above.
  2. 2.Two ends means a segment, one end means a ray, none means a line.
  3. 3.For a pair of lines, ask if they never meet, cross once, or cross at a square corner.

✍️ Try it

Kavya draws a straight mark with a dot at one end and an arrowhead at the other. What is it? Then: which one can you measure end to end with a ruler, a line or a line segment?

One stopping end and one arrowhead means it is a ray. Only a line segment can be measured, because a line never stops.

⚠️ Watch out

You might be thinking that a ray and a line are the same, since both run on for ever. A ray has one end that stops, so it travels one way only. Swap the two and every question about counting rays comes out wrong.

🌟 Why this matters

A torch beam is a ray, a stretched skipping rope is a line segment, and railway tracks stay parallel. Builders check that two walls meet at a square corner before laying a single brick. Naming each piece is how you describe any shape to someone else.
Exam tip: Look for arrowheads first, because they settle line against ray in one glance.

3

Watch me solve one

Quanta solves it

“Watch how I think through one of these — then you try.”

THE PROBLEM

“A figure starts at ONE point and has an arrow on the other end. What is it?”

  1. 1

    Count the endpoints

    Just one fixed end; the other has an arrow. 📏

  2. 2

    Rule out the segment

    A segment has two fixed endpoints.

  3. 3

    Rule out the line

    A line has arrows on both ends.

  4. 4

    Answer ✓

    One endpoint, one arrow → ray.

Now you try one — same steps, different story 👇

4

See it in action

⚡ Time to play!

An arrow means "goes on forever"; a red dot means "stops here". Tap what each figure is.

FIGURE · ROUND 1 OF 3

Tap the name of this figure.

5

Quick check

✅ VERIFICATION

Which of these has NO length at all?

⚡ Finish the activity above first to answer.

Keep going!

Up next: Types of Angles

Acute · Right · Obtuse · Reflex.

Concept 2 of 9 →