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Q11(iii):
State whether the following are true or false. Justify your answer. (iii) $\cos A$ is the abbreviation used for the cosecant of angle $A$.
Solution :
Given: The statement "$\cos A$ is the abbreviation used for the cosecant of angle $A$."
To Find: Determine whether the given statement is True or False and provide a mathematical justification.
Step 1: Defining Trigonometric Abbreviations
In trigonometry, the six primary trigonometric functions are defined by specific abbreviations derived from the names of the ratios of sides in a right-angled triangle. Let us define them formally:
- $\sin A$: Abbreviation for sine of angle $A$.
- $\cos A$: Abbreviation for cosine of angle $A$.
- $\tan A$: Abbreviation for tangent of angle $A$.
- $\cot A$: Abbreviation for cotangent of angle $A$.
- $\sec A$: Abbreviation for secant of angle $A$.
- $\csc A$ (or $\text{cosec } A$): Abbreviation for cosecant of angle $A$.
Step 2: Analyzing the Statement
The statement claims that $\cos A$ is the abbreviation for the cosecant of angle $A$. Based on the definitions established in Step 1:
1. The abbreviation $\cos A$ corresponds to the cosine of angle $A$.
2. The abbreviation for the cosecant of angle $A$ is $\csc A$ or $\text{cosec } A$.
Step 3: Logical Comparison
Since $\cos A$ represents the cosine function and not the cosecant function, the statement provided is mathematically incorrect. The term "cosecant" is the reciprocal of the sine function ($\csc A = \frac{1}{\sin A}$), whereas "cosine" is a distinct trigonometric ratio ($\cos A = \frac{\text{adjacent side}}{\text{hypotenuse}}$).
Conclusion:
The statement is False because $\cos A$ is the abbreviation for the cosine of angle $A$, while the abbreviation for the cosecant of angle $A$ is $\text{cosec } A$.
Final Answer: False. $\cos A$ is the abbreviation for the cosine of angle $A$, whereas the abbreviation for the cosecant of angle $A$ is $\text{cosec } A$.
More Questions from Class 10 Mathematics Introduction to Trigonometry EXERCISE 8.1
- Q1(i): In $\triangle ABC$, right-angled at $B$, $AB = 24$ cm, $BC = 7$ cm. Determine : (i) $\sin A, \cos A$
- Q1(ii): In $\triangle ABC$, right-angled at $B$, $AB = 24$ cm, $BC = 7$ cm. Determine : (ii) $\sin C, \cos C$
- Q10: In $\triangle PQR$, right-angled at $Q$, $PR + QR = 25$ cm and $PQ = 5$ cm. Determine the values of $\sin P, \cos P$ and $\tan P$.
- Q11(i): State whether the following are true or false. Justify your answer. (i) The value of $\tan A$ is always less than 1.
- Q11(ii): State whether the following are true or false. Justify your answer. (ii) $\sec A = \frac{12}{5}$ for some value of angle $A$.
- Q11(iv): State whether the following are true or false. Justify your answer. (iv) $\cot A$ is the product of cot and $A$.
- Q11(v): State whether the following are true or false. Justify your answer. (v) $\sin \theta = \frac{4}{3}$ for some angle $\theta$.
- Q2: In Fig. 8.13, find $\tan P – \cot R$.
- Q3: If $\sin A = \frac{3}{4}$, calculate $\cos A$ and $\tan A$.
- Q4: Given $15 \cot A = 8$, find $\sin A$ and $\sec A$.
- Q5: Given $\sec \theta = \frac{13}{12}$, calculate all other trigonometric ratios.
- Q6: If $\angle A$ and $\angle B$ are acute angles such that $\cos A = \cos B$, then show that $\angle A = \angle B$.
- Q7(i): If $\cot \theta = \frac{7}{8}$, evaluate : (i) $\frac{(1 + \sin \theta) (1 - \sin \theta)}{(1 + \cos \theta) (1 - \cos \theta)}$
- Q7(ii): If $\cot \theta = \frac{7}{8}$, evaluate : (ii) $\cot^2 \theta$
- Q8: If $3 \cot A = 4$, check whether $\frac{1 - \tan^2 A}{1 + \tan^2 A} = \cos^2 A – \sin^2 A$ or not.
- Q9(i): In triangle ABC, right-angled at B, if $\tan A = \frac{1}{\sqrt{3}}$, find the value of: (i) $\sin A \cos C + \cos A \sin C$
- Q9(ii): In triangle ABC, right-angled at B, if $\tan A = \frac{1}{\sqrt{3}}$, find the value of: (ii) $\cos A \cos C – \sin A \sin C$
CBSE Solutions for Class 10 Mathematics Introduction to Trigonometry
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