Question

cos15°+sin75°的值是______

cos15°+sin75°的值是______．

Answer 1

cos15°+sin75°=cos（45°-30°）+sin（45°+30°）=cos45°cos30°+sin45°sin30°+sin45°cos30°+cos45°sin30° = 2 2 × 3 2 + 2 2 × 1 2 + 2 2 × 3 2 + 2 2 × 1 2 = 6 + 2 2 ． 故答案为： 6 + 2 2 ．

Answer 2

cos15*sin75=cos15*cos15=(cos15)的平方
有二倍角公式的推理的(cos15)的平方=(1+cos30)/2=(1+根号3)/4