NCERT Mathematics, Class 10, textbook pages 73–98

How to help your child with Class 10 Maths Chapter 6, Triangles, at home

Similarity of triangles, explained for parents: a 45-minute study session, a quick challenge, a 5-day plan and the mistakes to watch for.

ADEBCDE ∥ BCAD/DB = AE/EC

NCERT Class 10 Maths Chapter 6 Triangles: what it teaches

Two triangles are similar if they have the same shape. Your teen learns the Basic Proportionality Theorem, the AA, SSS and SAS similarity criteria, and uses similarity to find unknown heights and lengths.

Why it matters later. Similarity underpins trigonometry (Chapters 8–9) and coordinate geometry.

See it: this chapter in pictures

AD/DB = AE/EC2/3 = 4/ECEC = 6
Parallel lines divide sides proportionally.
1 m0.8 m? m12 m
Similar triangles give the tree’s height: 15 m.
AA, SSS, SASsimilarity criteriasame shape, any size
Similar is not the same as congruent.

You need

  • ruler and protractor
  • a torch or sunlight and a stick
  • graph paper

Tonight’s 45 minutes

  1. Draw a triangle, draw a line parallel to one side, and measure the ratios (BPT).
  2. Measure a stick and its shadow, then a tree’s shadow, to find the tree’s height.
  3. Test AA similarity with two triangles of equal angles but different sizes.
  4. Solve: DE ∥ BC with AD = 2, DB = 3, AE = 4; find EC (6).

Words to use

  • similar
  • proportional
  • BPT
  • AA
  • SSS
  • SAS

Watch for

  • Matching the wrong corresponding sides. Match by angles first; write the correspondence in order.
  • Confusing similarity and congruence. Similar: same shape; congruent: same shape and size.

What it sounds like at home

A short example of the conversation. Your words will differ; the questions are what matter.

YouStick 1 m, shadow 0.8 m; tree shadow 12 m?

Your child12 ÷ 0.8 = 15 m.

A game for this week: Shadow height

  1. Measure a stick and its shadow.
  2. Measure shadows of tall objects.
  3. Calculate heights.
  4. Check plausibility.

A 5-day plan, 45 minutes a day

  1. Day 1Explain-back.
  2. Day 2Worked examples.
  3. Day 3Practice set.
  4. Day 4Real-life problem.
  5. Day 5Mixed quiz.

Everyday moments to practise

  • Map scales.
  • Shadow heights.
  • Photo enlargements.
  • Model making.

Quick check

Ask these at the end of the week. Tap to see the answer.

DE ∥ BC, AD = 2, DB = 3, AE = 4. EC?

6.

Are all equilateral triangles similar?

Yes.

Stick 1 m, shadow 0.8 m; tree shadow 12 m. Tree height?

15 m.

Ready for the next chapter when your child…

  • States and applies BPT.
  • Uses AA, SSS, SAS similarity.
  • Solves height and distance problems.

Activities, wording and illustrations are Mathify Kids’ own, following the topics of NCERT’s Mathematics (Class 10). See the full Class 10 parent guide for every chapter.

Questions parents ask

What is the Basic Proportionality Theorem?

A line parallel to one side of a triangle divides the other two sides in the same ratio.

Which criteria prove similarity?

AA, SSS and SAS.

Is Pythagoras proof included?

Check the current syllabus; similarity-based results are central.