cos15°=
(1+cos30°)2
(1-cos30°)2
±(1+cos30°)2
±(1-cos30°)2
Find the value of cos(15°):
As we know,
cos30°=cos2×15°
⇒ cos30°=2cos215°-1 [∵cos2θ=2cos2θ-1]
⇒ 2cos215°=1+cos30°
⇒ cos215°=1+cos30°2
∴cos2(15°)=1+cos(30°)2
Hence, Option(A) is correct.