# prove that: cos (2 x 30°) = 1 – tan 2 30 ° 1 + tan 2 30 ° - Mathematics

Sum

prove that:

cos (2 x 30°) = (1 – tan^2 30°)/(1+tan^2 30°)

#### 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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#### APPEARS IN

Selina Concise Mathematics Class 9 ICSE
Chapter 23 Trigonometrical Ratios of Standard Angles [Including Evaluation of an Expression Involving Trigonometric Ratios]
Exercise 23 (A) | Q 4.2 | Page 291