Introduction to Trigonometry

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NCERT Revision Notes for Chapter 8 Introduction to Trigonometry Class 10 Maths

CBSE NCERT Revision Notes

1

Trigonometry and Trigonometric Ratios

Answer

Trigonometry

Trigonometry is the branch of mathematics which deals with measurements of angles and the problems related to relationship between sides and angles.

Trigonometric Ratios:

It is the ratios of two sides of a right angle triangle.

Suppose we have a right angled triangle ABC.

 

Thus the trigonometric Ratios are defined as

The largest side of a right angle triangle is known as hypotenuse. Also, by Pythagoras theorem, we know that  h2 =b2+p2.

Here, θ is pronounced as theta,  ∠A=θ. We write trigonometric ratios according to angle θ.

2

Trigonometric Ratios for Few Particular Angels

Answer


Note:- Some Angles like cosecθ for θ=0o is not defined. We know that cosecθ = 1/ Sinθ = 1/0.  1/0 is not defined hence cosec0o is not defined. 

3

Trigonometric Identities 

Answer

 Identities are equations which are valid for any conditions. Trigonometric identities are equations involving trigonometric ratios.

Some Trigonometric Identities are 

Sin2θ+cos2⁡θ=1



Sec2θ-tan2⁡θ=1


Cosec2θ-cot2⁡θ=1

4

Trigonometric Ratios for Complementary Angles

Answer

sin (90 – θ) = cosθ

cos (90 – θ) = sinθ

tan (90 – θ) = cotθ

cot (90 – θ) = tanθ

sec (90 – θ) = cosecθ

cosec (90 – θ) = secθ

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