prove that cos2° 72° - sin 54 degrees = √5/4
Answers
Answered by
2
Answer:
Here, we will use, sin18∘=5–√−14
sin2(72∘)−sin2(60∘)
=sin2(90∘−18∘)−sin2(60∘)
=cos2(18∘)−sin2(60∘)
=1−sin2(18∘)−sin2(60∘)
Putting values of sin18∘andsin60∘
=1−(5–√−14)2−(3–√2)2
=1−(6−25–√16)−34
=16−6+25–√−1216
=25–√−216
∴sin2(72∘)−sin2(60∘)=5–√−18
Similar questions