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Cos22.5

sin(22.5+22.5)=根号2/2 sin45=2sin22.5*cos22.5(这个是正弦倍角公式,即sin 2a=2sina*cosa) sin22.5*cos22.5=根号2/4 cos22.5=根号(1-sin^2 22.5) sin22.5*根号(1-sin^2 22.5)=根号2/4

令a=22.5度 则cos2a=cos45=√2/2 cos2a=2cos²a-1=√2/2 cos²a=(2+√2)/4 显然cosa>0 所以cosa=√(2+√2)/2

解: cos22.5° =cos(45°/2) =√[(1+cos45°)/2] =√[(1+√2/2)/2] =√(2+√2)/2

0.923879532511286

(sin22.5+cos22.5)² =sin²22.5+cos²22.5+2sin22.5cos22.5 =1+sin22.5×2 =1+sin45º =1+√2/2 这是我在静心思考后得出的结论, 如果能帮助到您,希望您不吝赐我一采纳~(满意回答) 如果不能请追问,我会尽全力帮您解决的~ 答...

√2/2 √(2+√2)/2 √(√(2+√2)+2)/2 √是根号下 ≈ 0.707 0.924 0.981

约等于0.35355

原式=1/2(2sin22.5°cos22.5°) =1/2*sin45° =√2/4

cos15° =cos(45°-30°) =cos45°cos30°+sin45°sin30° =√2/2*√3/2+√2/2*1/2 =(√6+√2)/4 ∵cos15°=邻边/斜边 ∴斜边为: 22.5÷cos15° =90/(√6+√2) =45(√6-√2)/2

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