NCERT Mathematics, Class 11, textbook pages 43–75

How to help your child with Class 11 Maths Chapter 3, Trigonometric Functions, at home

Radians, trig functions of any angle and identities, explained for parents: a 45-minute study session, a quick challenge, a 5-day plan and the mistakes to watch for.

(cos θ, sin θ)π rad = 180°ASTC signs

NCERT Class 11 Maths Chapter 3 Trigonometric Functions: what it teaches

Trigonometry extends beyond right triangles: angles in radians, trig functions for any angle via the unit circle, their graphs and signs in quadrants, and identities like sin(A + B).

Why it matters later. Trigonometric functions are used in calculus, physics (waves) and Class 12 inverse trigonometry.

See it: this chapter in pictures

60° = π/3 rad5π/6 rad = 150°× π/180 or × 180/π
π rad = 180°.
sin 210°third quadrant: sin < 0= −½
ASTC tells the sign.
cos 15° = cos(45° − 30°)= cos45 cos30 + sin45 sin30= (√6 + √2)/4
Build new values from known ones.

You need

  • a compass and protractor
  • graph paper
  • a calculator in radian mode

Tonight’s 45 minutes

  1. Convert 60° to radians (π/3) and 5π/6 to degrees (150°).
  2. Draw a unit circle and mark (cos θ, sin θ) for 30°, 120°, 210°.
  3. Use ASTC to find signs in each quadrant.
  4. Derive cos 15° from cos(45° − 30°).

Words to use

  • radian
  • unit circle
  • period
  • quadrant
  • compound angle
  • identity

Watch for

  • Calculator in degree mode for radian problems. Check the mode before calculating.
  • Sign errors in quadrants. Use All-Sin-Tan-Cos for positive functions.

What it sounds like at home

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

Yousin 210°?

Your childThird quadrant, sin negative: −sin 30° = −½.

A game for this week: Unit circle quiz

  1. Draw a large unit circle.
  2. Call angles in degrees or radians.
  3. Players give sin and cos with signs.
  4. Check on the circle.

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

  • Sound and light waves.
  • Ferris wheel heights.
  • Tides.
  • AC electricity.

Quick check

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

60° in radians?

π/3.

sin 210°?

−½.

cos 15°?

(√6 + √2)/4.

Ready for the next chapter when your child…

  • Converts degrees and radians.
  • Finds trig values of any angle.
  • Uses compound angle identities.

Activities, wording and illustrations are Mathify Kids’ own, following the topics of NCERT’s Mathematics (Class 11). See the full Class 11 parent guide for every chapter.

Questions parents ask

What is a radian?

The angle for an arc equal to the radius; π radians = 180°.

Why use radians?

They make calculus formulas simple.

How to remember signs?

All (I), Sin (II), Tan (III), Cos (IV).