根号{1/2+[1/2*根号(1+cos2a)/2]},a∈(3π/2,2π)

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根号{1/2+[1/2*根号(1+cos2a)/2]},a∈(3π/2,2π)
根号{1/2+[1/2*根号(1+cos2a)/2]},a∈(3π/2,2π)

根号{1/2+[1/2*根号(1+cos2a)/2]},a∈(3π/2,2π)
根号{1/2+[1/2*根号(1+cos2a)/2]},a∈(3π/2,2π)
=√{1/2+(1/2)*√[(1+cos2a)/2]}
=√{1/2+(1/2)*√[1+2(cosa)^2-1]/2}
=√[1/2+(1/2)*√(cosa)^2]
a∈(3π/2,2π) cosa>0
=√[[1/2+(1/2)*cosa]
=√[(1+cosa)/2]
=√{1+2[cos(a/2)]^2-1}/2
=√(cosa/2)^2
a∈(3π/2,2π)
a/2∈(3π/4,π)
cosa/2