Trigonometrical Ratios Class 9 ICSE Important Questions with Answers
The 13 questions below are Trigonometrical Ratios Class 9 ICSE important questions, each with a full step-by-step answer: extra questions beyond the textbook exercises, covering 5 topics of ICSE Class 9 Maths in the question formats used in the exam.
By The Classmate AI Editorial Team
Reviewed by Classmate AI Team · 17 October 2026
Last updated 25 October 2026
- 13
- Questions
- 5
- Topics
- 4
- Key concepts
- ₹0
- With answers
ICSE Class 9 Trigonometrical Ratios questions ask you to write sin θ,cos θ,tan θ and their reciprocals csc θ,sec θ,cot θ from the sides of a right triangle, find all ratios given one ratio using the Pythagoras theorem, evaluate expressions and solve simple right-triangle problems. Remember sin θ=opp/hyp, cos θ=adj/hyp, tan θ=opp/adj.
About Trigonometrical Ratios
In the ICSE Class 9 Maths chapter Trigonometrical Ratios you define the six ratios sine, cosine, tangent, cosecant, secant and cotangent of an acute angle using the sides of a right-angled triangle. You learn the reciprocal and quotient relations, find the remaining ratios when one is given, and evaluate expressions. This Selina-aligned chapter builds the foundation for standard angles and the solution of right triangles.
Key concepts & formulas
For an acute angle θ in a right triangle, sin θ=opposite/hypotenuse, cos θ=adjacent/hypotenuse, tan θ=opposite/adjacent.
csc θ=1/(sin θ), sec θ=1/(cos θ), cot θ=1/(tan θ).
tan θ=(sin θ)/(cos θ) and cot θ=(cos θ)/(sin θ).
In a right triangle, (hypotenuse)²=(opposite)²+(adjacent)²; use it to find the third side before writing the ratios.
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Trigonometrical Ratios Questions and Answers
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MCQs with answers (1 mark)
In a right triangle, sin θ is equal to:
- (a)
adjacent/hypotenuse
- (b)
opposite/hypotenuse
- (c)
opposite/adjacent
- (d)
hypotenuse/opposite
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Answer: (b) opposite/hypotenuse.
By definition, the sine of an acute angle is the ratio of the side opposite the angle to the hypotenuse.
The reciprocal of cos θ is:
- (a)
sin θ
- (b)
cot θ
- (c)
sec θ
- (d)
csc θ
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Answer: (c) sec θ.
By definition sec θ=1/(cos θ).
If sin θ=3/5, then cos θ equals:
- (a)
4/5
- (b)
5/4
- (c)
3/4
- (d)
5/3
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Answer: (a) 4/5.
With opposite =3, hypotenuse =5, adjacent =√(5²-3²)=√16=4, so cos θ=4/5.
The value of tan θ × cot θ is:
- (a)
0
- (b)
1
- (c)
sin θ cos θ
- (d)
tan²θ
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Answer: (b) 1.
Since cot θ=1/(tan θ), we get tan θ × cot θ=tan θ × 1/(tan θ)=1.
Assertion–Reason questions (1 mark)
Assertion (A): For an acute angle θ, the value of sin θ is always less than 1.
Reason (R): In a right triangle the hypotenuse is the longest side, so the side opposite an acute angle is shorter than the hypotenuse.
- (a)
Both A and R are true and R is the correct explanation of A
- (b)
Both A and R are true but R is not the correct explanation of A
- (c)
A is true but R is false
- (d)
A is false but R is true
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Answer: (a) Since sin θ=opposite/hypotenuse and the opposite side is shorter than the hypotenuse, sin θ<1. R correctly explains A.
Very short answer questions (2 marks)
In right triangle ABC, right-angled at B, AB=8 cm, BC=6 cm and AC=10 cm. Write sin C and cos C.
Show model answer
For angle C: the opposite side is AB=8 cm, the adjacent side is BC=6 cm, and the hypotenuse is AC=10 cm.
sin C=AB/AC=8/10=4/5.
cos C=BC/AC=6/10=3/5.
If tan θ=5/12, find sin θ and cos θ.
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Take opposite =5 and adjacent =12. Then hypotenuse =√(5²+12²)=√(25+144)=√169=13.
sin θ=5/13 and cos θ=12/13.
Short answer questions (3 marks)
In the right triangle shown, right-angled at B, AB=12 cm and BC=5 cm. Find all six trigonometrical ratios of angle A.
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For angle A: opposite side =BC=5 cm, adjacent side =AB=12 cm.
Hypotenuse AC=√(AB²+BC²)=√(12²+5²)=√(144+25)=√169=13 cm.
sin A=5/13, cos A=12/13, tan A=5/12,
csc A=13/5, sec A=13/12, cot A=12/5.
If cos θ=7/25, evaluate (sin θ-cos θ)/(sin θ+cos θ).
Show model answer
With adjacent =7, hypotenuse =25, opposite =√(25²-7²)=√(625-49)=√576=24.
So sin θ=24/25, cos θ=7/25.
(sin θ-cos θ)/(sin θ+cos θ)=24/25-7/2524/25+7/25=17/2531/25=17/31.
If 5 sin θ=3, find the value of (sec θ+tan θ)/(sec θ-tan θ).
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5 sin θ=3⇒ sin θ=3/5, so opposite =3, hypotenuse =5, adjacent =√(5²-3²)=4.
Then cos θ=4/5, sec θ=5/4, tan θ=3/4.
(sec θ+tan θ)/(sec θ-tan θ)=5/4+3/45/4-3/4=8/42/4=8/2=4.
Long answer questions (5 marks)
In right triangle PQR, right-angled at Q, PQ=24 cm and PR=25 cm. (i) Find QR. (ii) Write all six trigonometrical ratios of angle R. (iii) Verify that tan R=(sin R)/(cos R).
Show model answer
(i) By Pythagoras, QR=√(PR²-PQ²)=√(25²-24²)=√(625-576)=√49=7 cm.
(ii) For angle R: opposite =PQ=24, adjacent =QR=7, hypotenuse =PR=25.
sin R=24/25, cos R=7/25, tan R=24/7,
csc R=25/24, sec R=25/7, cot R=7/24.
(iii) (sin R)/(cos R)=24/25/7/25=24/7=tan R. Verified.
If cot θ=15/8, find the values of (i) sin θ and cos θ, and (ii) evaluate (1+sin θ)(1-sin θ)/(1+cos θ)(1-cos θ).
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(i) cot θ=adjacent/opposite=15/8, so adjacent =15, opposite =8.
Hypotenuse =√(15²+8²)=√(225+64)=√289=17.
sin θ=8/17, cos θ=15/17.
(ii) (1+sin θ)(1-sin θ)=1-sin²θ=1-(8/17)²=1-64/289=225/289.
(1+cos θ)(1-cos θ)=1-cos²θ=1-(15/17)²=1-225/289=64/289.
Ratio =225/289/64/289=225/64.
Case study questions (4 marks)
A ladder leans against a wall forming a right-angled triangle with the ground. The foot of the ladder is 9 m from the wall (adjacent side) and the ladder reaches 12 m up the wall (opposite side). Let θ be the angle the ladder makes with the ground.
(i) Find the length of the ladder (the hypotenuse).
(ii) Write sin θ and cos θ.
(iii) Find tan θ.
(iv) Show that sin²θ+cos²θ=1.
Show model answer
(i) Ladder length =√(9²+12²)=√(81+144)=√225=15 m.
(ii) sin θ=opposite/hypotenuse=12/15=4/5; cos θ=adjacent/hypotenuse=9/15=3/5.
(iii) tan θ=opposite/adjacent=12/9=4/3.
(iv) sin²θ+cos²θ=(4/5)²+(3/5)²=16/25+9/25=25/25=1.
Continues in Class 10: Trigonometrical Identities Class 10 ICSE questions
All ICSE Class 9 Maths Chapters
Frequently asked questions
What are the six trigonometric ratios in ICSE Class 9?
sin θ=opp/hyp, cos θ=adj/hyp, tan θ=opp/adj, and their reciprocals csc θ, sec θ and cot θ. Also tan θ=(sin θ)/(cos θ). This page has 13 questions using them, with answers. Learn the three main ratios well; the other three are just their reciprocals.If tan θ = 5/12, how do you find sin θ and cos θ?
Draw a right triangle with opposite side 5 and adjacent side 12; by Pythagoras the hypotenuse is 13. So sin θ=5/13 and cos θ=12/13. The same method works whichever ratio is given.If 5 sin θ = 3, what is (sec θ + tan θ)/(sec θ − tan θ)?
sin θ=3/5, so the triangle is 3, 4, 5: sec θ=5/4 and tan θ=3/4. The expression is 2/1/2=4. Find each ratio first, then substitute. Simplifying the numerator and denominator separately before dividing keeps the fractions manageable.Why is sin θ always less than 1 for an acute angle?
Because sin θ is the opposite side divided by the hypotenuse, and the hypotenuse is the longest side of a right triangle. The same is true for cos θ. tan θ, however, can be more than 1.Which ICSE Class 9 trigonometry chapters follow Trigonometrical Ratios?
Trigonometrical Ratios of Standard Angles (Chapter 23), Solution of Right Triangles (Chapter 24) and Complementary Angles (Chapter 25). Trigonometrical Ratios is Chapter 22; each later chapter has its own important-questions page.How do I avoid mixing up opposite and adjacent sides?
Mark the angle θ first, label the side facing it 'opposite', the side touching it (not the hypotenuse) 'adjacent', and the longest side 'hypotenuse'. Relabel every time the angle changes, since opposite and adjacent swap.Can I download Trigonometrical Ratios ICSE Class 9 questions?
Yes. Enter your email in the free PDF box on this page and all 13 ratio questions, the ladder case study included, open with answers as a printable worksheet.
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