Chapter 15 · Class 9 ICSE · Formula Sheet
Trigonometric Ratios Formulas — Class 9 ICSE
Define sine, cosine, and tangent ratios and solve problems involving right triangles.
Key Formulas
sin
\sin\theta = \dfrac{\text{Opp}}{\text{Hyp}}
cos
\cos\theta = \dfrac{\text{Adj}}{\text{Hyp}}
tan
\tan\theta = \dfrac{\text{Opp}}{\text{Adj}}
Identity
\sin^2\theta + \cos^2\theta = 1
Standard Values
\sin 30° = \dfrac{1}{2}, \quad \sin 45° = \dfrac{\sqrt{2}}{2}, \quad \sin 60° = \dfrac{\sqrt{3}}{2}
Worked Examples
1Using: sin 30
Find sin 30 + cos 60.
Step 1: sin 30 = 1/2, cos 60 = 1/2.
Step 2: Sum = 1/2 + 1/2 = 1.
Answer: 1
2Using: tan identity
If tan A = 3/4, find sin A.
Step 1: In right triangle: opposite = 3, adjacent = 4.
Step 2: hypotenuse = 5. sin A = 3/5.
Answer: 3/5
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