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sin2 θ + cos2 θ = 1
sin (A ± B) = sin A cos B ± cos A sin B
cos (A ± B) = cos A cos B ± sin A sin B
sin A ± sin B = 2 sin[1/2(A ± B)] cos[1/2(A ± B)]
If l θ l <<1, then
cos θ ≈ 1 and tan θ ≈ sin θ ≈ θ (θ in radians)
Small Angle Formula
Small Angle Formula
In the two forms of the small-angle formula shown here, the distance and physics size must be in the same units. The angular size must be in degrees.
Note: In addition to calculating sizes, this formula can also be used to determine the separation between two objects.
The second form of the small-angle formula, is solved for the physical size of the object.
S = physical size of the object
d = distance to the object
α = angular size of the object in arc seconds
If the angular size is given in degrees, this formula should be used.
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