Question

PLEASE DO IT.....IT'S URGENT​

Answer 1

cos 2A = 2cos² A - 1

=> if , A = 30°

then ,

=> cos ( 2×30° ) = 2 cos² 30° - 1

=> cos 60° = 2cos² 30° - 1

=> 1/2 = 2cos² 30° - 1 { since , cos 60° = 1/2 }

=> 1/2 + 1 = 3/2 = 2cos² 30°

=> 3/4 = cos² 30°

=> √ ( 3/4 ) = cos² 30°

=> ± √3 / 2 = cos 30°

• 30° being in first quadrant , cos 30° is positive .

=> cos 30° = √3 / 2