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SAI International School
CLASS - X

Mathematics
CHAPTER-8 : Introduction to Trigonometry

Lesson Notes- 4

SUBTOPIC :Trigonometric Identities

Trigonometric Identities

An equation is said to be a trigonometric identity, if it contains trigonometric ratios of an
angle and satisfies for all values of ofthe given trigonometric ratios.

In ∆PQR, right angled at Q, ∠R = we can say that

2
2
2
PQ + QR = PR
2
Divide each term by PR , we get

2
2
(sin R) + (cos R) = 1
2
2
sin R + cos R =1

2
2
sin + cos = 1 ......... 1

Likewise other trigonometric identities can also be proved.

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