Answer:
The exact value of sin 22.5° using the half-angle formula is √(2 - √2) / 2 or 0.38
Step-by-step explanation:
Let us consider θ = 22.5 º
Therefore, sin2θ = [(1− cos 2θ) / 2] -------(1)
If θ = 22.5° then 2θ is 45°.
On substituting the value of θ in equation (1), we get
sin2 22.5° = [(1− cos (2 × 22.5°)) / 2]
sin2 22.5° = [(1− cos 45°) / 2]
sin2 22.5°= [ [1 - (1 / √2)] / 2 ]
sin2 22.5°= (2 - √2) / 4 [ on simplifying the above RHS value ]
sin 22.5° = [√(2 - √2) / 2]
After substituting the value of √2 as 1.414 in the above equation, we get
sin 22.5°= 0.38
