√{（1/2）+（1/2）√[（1/2）+（1/2）cos2α]} (cos2α = 2(cosα) -1) =√{(0.5+0.5√(0.5+0.5[2(cosα) -1])} =√{[0.5+0.5√(cosα)]} (因為3π/2＜α＜2π,α在第四象限,所以cosα > 0) =√{[0.5+0.5cosα]} (c...