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About Introduction to Trigonometry — Class 10 CBSE

Define trigonometric ratios, find values of standard angles, and prove trigonometric identities. This topic is part of the CBSE Class 10 mathematics syllabus (chapter: Chapter 8). On this page you can practice 60 questions across three difficulty levels — 20 easy, 20 medium, and 20 hard — each with a visual step-by-step solution, plus a timed 35-question mastery test with a live leaderboard. Worked examples and sample questions from the topic are below.

What you'll learn in Introduction to Trigonometry

  • Introduction to Trigonometry: The Basics
  • Trigonometric Ratios: Sine, Cosine, Tangent
  • Reciprocal Ratios and Inter-relationships
  • Trigonometric Ratios of Specific Angles
  • Trigonometric Identities and Summary

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

Introduction to Trigonometry — solved examples for Class 10 CBSE

Example 1easy

In a right-angled triangle ABC, right-angled at B, if AB = 8 cm and BC = 6 cm, what is the value of tan A?
  1. A)3/4
  2. B)4/3
  3. C)3/5
  4. D)4/5

Step-by-step solution

  1. Identify the sides relative to angle A. The side opposite to angle A is BC = 6 cm. The side adjacent to angle A is AB = 8 cm.
  2. Apply the definition of tan A.
    tanA=Opposite/Adjacenttan A = Opposite / Adjacent
  3. Substitute the given values.
    tanA=BC/AB=6/8tan A = BC / AB = 6 / 8
  4. Simplify the fraction.
    tanA=3/4tan A = 3 / 4

Answer: 3/4

Example 2medium

In a right-angled triangle ABC, right-angled at B, if AB = 7 cm and BC = 24 cm, what is the value of sin C?
  1. A)7/25
  2. B)24/25
  3. C)7/24
  4. D)24/7

Step-by-step solution

  1. Given a right-angled triangle ABC, with the right angle at B. AB = 7 cm, BC = 24 cm.
  2. Using the Pythagorean theorem, AC² = AB² + BC².
    AC2=72+242=49+576=625AC² = 7² + 24² = 49 + 576 = 625
  3. So, AC = √625 = 25 cm.
  4. For angle C, the side opposite is AB and the hypotenuse is AC. Therefore, sin C = Opposite/Hypotenuse = AB/AC.
    sinC=7/25sin C = 7/25

Answer: 7/25

Example 3hard

Which of the following statements is NOT possible for an acute angle A?
  1. A)sin A = (p² + 1) / (p² + 2) for some real p
  2. B)sec A = 1/2
  3. C)tan A = 20
  4. D)cos A = (q² - 1) / (q² + 1) for some real q where q ≠ 0

Step-by-step solution

  1. For an acute angle A, 0 < sin A < 1, 0 < cos A < 1, tan A > 0, sec A > 1, cosec A > 1, cot A > 0.
  2. Option A: sin A = (p² + 1) / (p² + 2). Since p² ≥ 0, p² + 1 < p² + 2. So, (p² + 1) / (p² + 2) is always less than 1. Also, since p² + 1 > 0 and p² + 2 > 0, sin A > 0. Thus, 0 < sin A < 1 is possible.
  3. Option B: sec A = 1/2. For an acute angle A, sec A is always greater than 1. Since 1/2 is less than 1, sec A = 1/2 is NOT possible.
  4. Option D: cos A = (q² - 1) / (q² + 1). For this to be a valid cosine value, -1 < cos A < 1. If q=1, cos A = 0. If q>1, 0 < cos A < 1. If 0<q<1, then q²-1 is negative, but q²+1 is positive, so cos A would be negative, which is not possible for an acute angle. However, the question states 'for some real q where q ≠ 0'. If q is real, q²-1 can be negative or positive. But for an acute angle A, cos A must be positive (0 < cos A < 1). If q=1, cos A = 0 (not acute). If q>1, then q²-1 is positive and q²-1 < q²+1, so 0 < cos A < 1, which is possible. Thus, this statement *can* be possible for certain q.

Answer: sec A = 1/2

Practice questions on Introduction to Trigonometry

  1. Q1.easy

    Which of the following statements about trigonometric ratios for an acute angle A is ALWAYS true?
    1. A)sin A > 1
    2. B)sec A < 1
    3. C)tan A can be greater than 1
    4. D)cos A can be 5/3
    Show answer

    Answer: tan A can be greater than 1

    Hint: Consider the definitions of sin, cos, tan, and sec in terms of sides of a right triangle. Remember that the hypotenuse is always the longest side.

  2. Q2.easy

    If sin θ = 12/13, what is the value of cosec θ?
    1. A)13/12
    2. B)5/12
    3. C)12/5
    4. D)1/13
    Show answer

    Answer: 13/12

    Hint: Recall the reciprocal relationship between sine and cosecant.

  3. Q3.easy

    Evaluate the expression: 2 × sin 30° + tan 45°.
    1. A)1
    2. B)2
    3. C)3/2
    4. D)5/2
    Show answer

    Answer: 2

    Hint: Recall the standard trigonometric values for 30° and 45°.

  4. Q4.medium

    If 3 cot A = 4, then the value of sin A is:
    1. A)4/5
    2. B)5/3
    3. C)3/5
    4. D)4/3
    Show answer

    Answer: 3/5

    Hint: From cot A, you can form a right-angled triangle using the ratio of adjacent to opposite sides. Then use Pythagoras theorem to find the hypotenuse.

  5. Q5.medium

    Evaluate: (sin 60° × cos 30° + sin 30° × cos 60°)
    1. A)0
    2. B)1/2
    3. C)1
    4. D)√3/2
    Show answer

    Answer: 1

    Hint: Recall the values of sine and cosine for the standard angles 30° and 60°. Substitute these values into the expression and simplify.

  6. Q6.medium

    Which of the following statements is INCORRECT?
    1. A)sin 0° = 0
    2. B)cos 90° = 0
    3. C)tan 45° = 1
    4. D)sec 0° = 0
    Show answer

    Answer: sec 0° = 0

    Hint: Recall the definitions and standard values of trigonometric ratios for 0° and 90°. Remember that secant is the reciprocal of cosine.

  7. Q7.hard

    If (sin θ + cos θ) / (sin θ - cos θ) = 3, then what is the value of sin⁴θ - cos⁴θ?
    1. A)1/5
    2. B)2/5
    3. C)3/5
    4. D)4/5
    Show answer

    Answer: 3/5

    Hint: First, use the given equation to find the value of tan θ. Then, express sin⁴θ - cos⁴θ in terms of tan θ or by simplifying it using algebraic identities.

  8. Q8.hard

    Evaluate: (cos²20° + cos²70°) / (sec²50° - cot²40°) + 2sin²30° - (1/2)cos²60°.
    1. A)1
    2. B)2
    3. C)2.25
    4. D)2.5
    Show answer

    Answer: 2

    Hint: Use complementary angle identities (e.g., cos(90°-A) = sin A, cot(90°-A) = tan A) and fundamental identities like sin²A + cos²A = 1 and sec²A - tan²A = 1. Also, recall the values of standard angles.

  9. Q9.hard

    If x = a sin θ and y = b cos θ, which of the following expressions must be true?
    1. A)b²x² + a²y² = a²b²
    2. B)a²x² + b²y² = a²b²
    3. C)x²/a² + y²/b² = 1
    4. D)x² + y² = a² + b²
    Show answer

    Answer: b²x² + a²y² = a²b²

    Hint: Rearrange the given equations to express sin θ and cos θ in terms of x, y, a, b. Then use the fundamental identity sin²θ + cos²θ = 1.

These are 9 of the 60 questions available for Introduction to Trigonometry. Start practicing above to unlock visual solutions, AI coaching, and the topic leaderboard — completely free.