Sum
prove that:
cos (2 x 30°) = `(1 – tan^2 30°)/(1+tan^2 30°)`
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Solution
RHS,
`(1 – tan^2 30°)/(1 +tan^2 30°) = (1–(1)/(3))/(1+(1)/(3)) = (1)/(2)`
LHS,
cos (2 x 30°) = `cos 60° = (1)/(2)`
LHS = RHS
Concept: Trigonometric Ratios of Some Special Angles
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