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Question
If A = 450 , verify that:
(ii) cos 2A = 2 cos2 A – 1 = 1 – 2 sin2 A
Solution
A= 450
`⇒ 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 A
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