# If a = 450 , Verify That: (Ii) Cos 2a = 2 Cos2 a – 1 = 1 – 2 Sin2 a - Mathematics

If A = 45, verify that:

(ii) cos 2A = 2 cos2 A – 1 = 1 – 2 sin2

#### Solution

A= 45

⇒ 2A = 2xx45^0=90^0

(ii) cos 2 A = cos 90^0 = 0

2 cos^2 -1 = 2 cos ^2 45 ^0-1 = 2 xx(1/sqrt(2))^2 -1=2 xx1/2 -=1-1=0

Now , 1-2 sin^2 A =1-2 xx(1/sqrt(2)^2 )-1=1-2xx1/2=1-1=0

∴  cos 2A = 2 cos2 A – 1 = 1 – 2 sin2

Concept: Trigonometric Ratios and Its Reciprocal
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#### APPEARS IN

RS Aggarwal Secondary School Class 10 Maths
Chapter 6 T-Ratios of some particular angles
Exercises | Q 12.2
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