How to find the exact values of cos 22.5^(circ) using the half-angle formula?

Trey Montes

Trey Montes

Answered question

2023-03-25

How to find the exact values of cos22.5° using the half-angle formula?

Answer & Explanation

Lindsey Ortega

Lindsey Ortega

Beginner2023-03-26Added 4 answers

Explanation:
Calculate the necessary value.
We have that, cosA=cos2A2-sin2A2
Here A=45°
cosA=cos2A2-1-cos2A2
cosA=2cos2A2-1
cos45°=2cos222.5°-1
1 2 + 1 = 2 cos 2 22.5   [ cos 45 = 1 2 ]
2 2 + 1 = 2 cos 2 22.5
2 + 2 4 = cos 2 22.5
cos 22.5 = ( 2 + 2 ) 2
cos 22.5 0.92
Thus, the exact value of cos 22.5 is ( 2 + 2 ) 2 or 0.92.

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