Let the given sum be
E. We can write the product of cosecants as:
E=∑m=16sin(θ+(m−1)4π)sin(θ+4mπ)1Multiplying and dividing by
sin(4π)=21, we get:
E=2∑m=16sin(θ+(m−1)4π)sin(θ+4mπ)sin((θ+4mπ)−(θ+(m−1)4π))E=2∑m=16[cot(θ+(m−1)4π)−cot(θ+4mπ)]This is a telescoping sum. Expanding the terms:
E=2[(cotθ−cot(θ+4π))+(cot(θ+4π)−cot(θ+42π))+⋯+(cot(θ+45π)−cot(θ+46π))]E=2[cotθ−cot(θ+23π)]Using the allied angle identity
cot(θ+23π)=−tanθ, we have:
E=2(cotθ+tanθ)=2(sinθcosθ+cosθsinθ)=sinθcosθ2=sin(2θ)22We are given that
E=42.
sin(2θ)22=42⇒sin(2θ)=21Since
θ∈(0,2π), we have
2θ∈(0,π). The solutions for
2θ are
6π and
65π.
Thus,
θ=12π,125π.
The largest element is
α=125π and the smallest is
β=12π.
The absolute difference is
α−β=125π−12π=124π=3π.
Answer:
3π