求cos(80°+2α)cos(65°+2α)+sin(80°+2α)sin(65°+2α)的值
题目
求cos(80°+2α)cos(65°+2α)+sin(80°+2α)sin(65°+2α)的值
答案
cos(80°+2α)cos(65°+2α)+sin(80°+2α)sin(65°+2α)
=cos[(80°+2α)-(65°+2α)]
=cos15°
=cos(45°-30°)
=cos45°cos30°+sin45°sin15°
=(√6+√2)/4
举一反三
已知函数f（x）=x，g（x）=alnx，a∈R．若曲线y=f（x）与曲线y=g（x）相交，且在交点处有相同的切线，求a的值和该切线方程．
我想写一篇关于奥巴马的演讲的文章,写哪一篇好呢?为什么好
最新试题
热门考点