Question

cosA + sinAis equal to
cosA - sin A
Option 1:
tan(45° - A)
Option 2:
tan(45° + A)
Option 3:
tan(90° - A)
Option 4:
tan A​

Answer 1

Answer:

Mathematics NCERT Grade 10, Chapter 8: Introduction to Trigonometry: In the beginning, a quote is given about trigonometry in an eye-catching way.  Some real-life examples like finding the height of Qutub Minar, finding the width of the river, and finding the altitude of the ground from the hot air balloon are given in order to explain the need for trigonometry. In this chapter, students will study the trigonometric ratios of the angle i.e ratios of the sides of a right triangle with respect to its acute angles. The discussion of the trigonometric ratios will be restricted to acute angles only.

In section 8.2 various trigonometric ratios are explained. Trigonometric ratios are given in this section:

SINE

COSINE

TANGENT

COSECANT

SECANT

COTANGENT

Solved examples are given to explain how to find trigonometric ratios and how to prove certain given relations.

Special note is given stating that the values of the trigonometric ratios of an angle do not vary with the lengths of the sides of the triangle if the angle remains the same.  

In exercise 8.1 students have to determine certain trigonometric ratios.

In the next section, trigonometric ratios of some specific angles are given. Value of ratios of angle 0°, 30°, 45°, 60°, 90° are given in table 8.1. Students must learn these values as they are the most important part of this chapter and are essential to solve the problems not only in this chapter but are useful in higher grades as well.

Exercise 8.2 contains 4 different types of questions based on trigonometric ratios.  

In section 8.4 trigonometric ratios of complementary angles are given. Total 6 relations are given in this section. These relations must be on the fingertips of students in order to score better. Exercise 8.3 is based on the same.  

The next part of the chapter is about trigonometric identities. Three important identities are highlighted in this section. These identities are true for all angles (A) such that A ∈[0°, 90°]. Using the same students will be able to solve the problems of exercise 8.4 including the problems which need certain given statements to prove. In the end key points of chapter are discussed.  

Page No 181:

Question 1:

In ΔABC right angled at B, AB = 24 cm, BC = 7 cm. Determine

(i) sin A, cos A

(ii) sin C, cos C

ANSWER:

Applying Pythagoras theorem for ΔABC, we obtain

AC2 = AB2 + BC2

= (24 cm)2 + (7 cm)2

= (576 + 49) cm2

= 625 cm2

∴ AC = 625 cm = 25 cm