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About Trigonometry — Class 10 ICSE

Prove trigonometric identities and solve problems on heights and distances. This topic is part of the ICSE Class 10 mathematics syllabus (chapter: Chapter 7). On this page you can practice 59 questions across three difficulty levels — 20 easy, 19 medium, and 20 hard — each with a visual step-by-step solution, plus a timed 34-question mastery test with a live leaderboard. Worked examples and sample questions from the topic are below.

What you'll learn in Trigonometry

  • Introduction to Trigonometric Ratios
  • Fundamental Trigonometric Identities
  • Strategies for Proving Trigonometric Identities
  • Applications: Heights and Distances
  • Advanced Identities & Exam Preparation

Interactive lesson · about 15 minutes · checkpoint question after every unit

Trigonometry — solved examples for Class 10 ICSE

Example 1easy

In a right-angled triangle ABC, right-angled at B, if we define sin A = BC/AC, which of the following statements is conceptually correct?
  1. A)AC is always the longest side.
  2. B)BC is the side adjacent to angle A.
  3. C)The value of sin A can be greater than 1.
  4. D)Angle C must be obtuse.

Step-by-step solution

  1. In a right-angled triangle, the side opposite the right angle (90°) is called the hypotenuse.
  2. The hypotenuse is always the longest side in a right-angled triangle.
  3. Since AC is the hypotenuse (opposite angle B, which is 90°), it must be the longest side.

Answer: AC is always the longest side.

Example 2medium

If tan A = 4/3, and A is an acute angle, what is the value of sin A + cos A?
  1. A)7/5
  2. B)1/5
  3. C)5/7
  4. D)2/5

Step-by-step solution

  1. Given tan A = Opposite/Adjacent = 4/3. Let the opposite side be 4k and the adjacent side be 3k.
  2. Using Pythagoras theorem, Hypotenuse² = (4k)² + (3k)² = 16k² + 9k² = 25k². So, Hypotenuse = 5k.
  3. Now, sin A = Opposite/Hypotenuse = 4k/5k = 4/5 and cos A = Adjacent/Hypotenuse = 3k/5k = 3/5.
  4. Therefore, sin A + cos A = 4/5 + 3/5 = 7/5.

Answer: 7/5

Example 3hard

If the expression (sec θ + tan θ - 1) / (tan θ - sec θ + 1) is simplified, which of the following expressions is it equivalent to?
  1. A)(1 + sin θ) / cos θ
  2. B)(1 - sin θ) / cos θ
  3. C)(1 + cos θ) / sin θ
  4. D)(1 - cos θ) / sin θ

Step-by-step solution

  1. Consider the numerator: sec θ + tan θ - 1. Substitute 1 = sec²θ - tan²θ. So, sec θ + tan θ - (sec²θ - tan²θ).
  2. Factorize: sec θ + tan θ - (sec θ - tan θ)(sec θ + tan θ) = (sec θ + tan θ) [1 - (sec θ - tan θ)] = (sec θ + tan θ) [1 - sec θ + tan θ].
  3. The expression becomes (sec θ + tan θ) [1 - sec θ + tan θ] / (tan θ - sec θ + 1). The term [1 - sec θ + tan θ] cancels out.
  4. Thus, the simplified expression is sec θ + tan θ, which is equal to 1/cos θ + sin θ/cos θ = (1 + sin θ)/cos θ.

Answer: (1 + sin θ) / cos θ

Practice questions on Trigonometry

  1. Q1.easy

    What is the exact value of (sin 45° × cos 45°) + tan 45°?
    1. A)1/2
    2. B)1
    3. C)3/2
    4. D)2
    Show answer

    Answer: 3/2

    Hint: Recall the values of trigonometric ratios for 45°: sin 45° = cos 45° = 1/√2 and tan 45° = 1.

  2. Q2.easy

    A student claimed that if tan(90° - A) = cot A is true, then sec(90° - A) must be equal to -cosec A. What is the error in the student's reasoning?
    1. A)The identity tan(90° - A) = cot A is incorrect.
    2. B)The sign of the trigonometric ratio does not change for complementary angles in the first quadrant.
    3. C)sec(90° - A) is actually equal to tan A.
    4. D)The complementary angle identities only apply to angles less than 45°.
    Show answer

    Answer: The sign of the trigonometric ratio does not change for complementary angles in the first quadrant.

    Hint: Remember that for acute angles (0° to 90°), all trigonometric ratios are positive.

  3. Q3.easy

    An observer is 100 meters away from the base of a tower. The angle of elevation to the top of the tower is 30°. Which trigonometric ratio would you use to directly find the height of the tower?
    1. A)sin 30°
    2. B)cos 30°
    3. C)sec 30°
    4. D)tan 30°
    Show answer

    Answer: tan 30°

    Hint: Draw a right-angled triangle. Identify the known side (adjacent to the angle) and the unknown side (opposite to the angle). Which ratio relates these two?

  4. Q4.medium

    Evaluate: (sin 30° + tan 45° - cosec 60°) / (sec 30° + cos 60° + cot 45°)
    1. A)(3√3 - 4) / (6 + 3√3)
    2. B)0
    3. C)1
    4. D)(1 - √3) / (1 + √3)
    Show answer

    Answer: 0

    Hint: Recall the exact values of trigonometric ratios for standard angles (30°, 45°, 60°) and substitute them into the expression.

  5. Q5.medium

    Simplify the expression: (1 - sin²A) / (1 - cos²A)
    1. A)tan²A
    2. B)cot²A
    3. C)sec²A
    4. D)cosec²A
    Show answer

    Answer: cot²A

    Hint: Remember the fundamental trigonometric identity sin²θ + cos²θ = 1. Use it to rewrite the numerator and the denominator.

  6. Q6.medium

    If sin 3A = cos (A - 26°), where 3A is an acute angle, find the value of A.
    1. A)29°
    2. B)30°
    3. C)31°
    4. D)32°
    Show answer

    Answer: 29°

    Hint: Use the complementary angle identity: sin θ = cos (90° - θ). Equate the angles after applying the identity.

  7. Q7.hard

    Given that A and B are complementary angles (A + B = 90°), what is the value of sin²A + sin²B + tan A tan B?
    1. A)0
    2. B)1
    3. C)2
    4. D)3
    Show answer

    Answer: 2

    Hint: Use complementary angle identities to express everything in terms of a single angle, then apply fundamental identities.

  8. Q8.hard

    Ravi was asked to prove the identity sin⁴θ + cos⁴θ = 1 - 2sin²θcos²θ. His steps are:
    1. L.H.S. = sin⁴θ + cos⁴θ
    2. = (sin²θ)² + (cos²θ)²
    3. = (sin²θ + cos²θ)² - 2sin²θcos²θ
    4. = 1² - 2sin²θcos²θ
    5. = 1 - 2sin²θcos²θ = R.H.S.
    Which of the following statements is true regarding Ravi's proof?
    1. A)Step 1 is incorrect.
    2. B)Step 3 uses an incorrect algebraic identity.
    3. C)The proof is entirely correct.
    4. D)Step 5 is not equivalent to R.H.S.
    Show answer

    Answer: The proof is entirely correct.

    Hint: Carefully recall the algebraic identity for a² + b² and the fundamental trigonometric identity sin²θ + cos²θ = 1.

  9. Q9.hard

    A man on the top of a tower 100 m high observes a car moving towards the tower at an angle of depression of 30°. After some time, the angle of depression becomes 60°. What is the distance travelled by the car during this time?
    1. A)100√3 m
    2. B)200/√3 m
    3. C)100(√3 - 1) m
    4. D)200√3 m
    Show answer

    Answer: 200/√3 m

    Hint: Draw two right-angled triangles. Use the tangent ratio for both angles of depression to find the initial and final distances of the car from the tower.

These are 9 of the 59 questions available for Trigonometry. Start practicing above to unlock visual solutions, AI coaching, and the topic leaderboard — completely free.