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प्रश्न
If A = 30°, verify that `cos 2A = (1 - tan^2A)/(1 + tan^2A)`.
योग
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उत्तर
A = 300
⇒ 2A = 2 × 300 = 600
cos 2A = cos `60^0 = 1/2`
`(1- tan62 A)/(1+ tan^2 A) = (1-tan^2 30^0)/(1+ tan^2 30^0)= (1-(1/sqrt(3))^2)/(1+(1/sqrt(3))^2` = `(1-(1/3))/(1+(1/3)) = ((2/3))/(4/3) = (2/3)xx3/4=1/2`
∴ cos 2A = `(1-tan^2A)/(1+ tan^2A)`
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अध्याय 11: T-Ratios of Some Particular Angles - EXERCISE 11 [पृष्ठ ५७२]
