what is the value of Cos 36° ?
In detail.......
Answers
Answered by
4
Answer:
If you calculate it aiding 991ES calculator then the answer comes to
0.809016...(approx)
Answered by
54
To find:-
cos36° = ?
Solution:-
Let β = 18° .Then,
β = 18° => 5β = 90°
⠀⠀⠀ ⠀=> 3β+2β = 90°
⠀⠀⠀ ⠀=> 2β = 90° - 3β
⠀⠀ ⠀⠀=> sin2β = sin(90°-3β) = cos3β
⠀⠀⠀⠀ => 2sinβ cosβ = 4cos³β - 3cosβ
⠀ ⠀=> 2sinβcosβ - 4cos³β + 3cosβ = 0
⠀⠀⠀⠀ => cosβ(2sinβ - 4cos²β + 3) = 0
⠀⠀ ⠀⠀=> 2sinβ - 4cos²β + 3 = 0
⠀⠀⠀⠀ => 2sinβ - 4(1-sin²β) + 3 = 0
⠀⠀ ⠀=> 4sin²β + 2sinβ -1 = 0
According to Sri Dharacharya formula
⠀⠀⠀⠀
As we are supposed that β= 18°
Then,
Now for cos18°
=> cos36° = cos(2×18) = (1 - 2sin²18°)
=> cos36° =
Hence proved.❤
Hope its help uh❤
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