题目
sin(x- 3π/4)cos(x- π/4)=—1/4 求cos4x
提问时间:2021-03-19
答案
sin(x- 3π/4)
=sin(x-π/4-π/2)
=-sin[π/2-(x-π/4)]
=-cos(x-π/4)
所以由已知,
-cos(x- π/4)^2=—1/4
所以cos(x-π/4)^2=1/4
所以cos2(x-π/4)=2cos(x-π/4)^2-1
=-1/2
所以
cos4x
=-cos4(x-π/4)
=-[2cos2(x-π/4)^2-1]
=-[2*(-1/2)^2-1]
=1/2
好好学习,天天向上,呵呵!
=sin(x-π/4-π/2)
=-sin[π/2-(x-π/4)]
=-cos(x-π/4)
所以由已知,
-cos(x- π/4)^2=—1/4
所以cos(x-π/4)^2=1/4
所以cos2(x-π/4)=2cos(x-π/4)^2-1
=-1/2
所以
cos4x
=-cos4(x-π/4)
=-[2cos2(x-π/4)^2-1]
=-[2*(-1/2)^2-1]
=1/2
好好学习,天天向上,呵呵!
举一反三
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
奥巴马演讲不用看稿子.为什么中国领导演讲要看?
想找英语初三上学期的首字母填空练习……
英语翻译
1,人们染上烟瘾,最终因吸烟使自己丧命.
最新试题
- 1表达浓浓的乡情的诗
- 212和6和3怎样算等于1?
- 3甲乙两车同时从a、b两地出发,相向而行.在距两地中点40千米处相遇,已知甲乙两车的速度比是7:5,两地相距
- 4读了《尊重卑微》你能想到哪些人,那些事,用一两句话说一说
- 5英语翻译Honor old people as we do our own aged parents.
- 6若关于x的方程(k+1)x的/k/+1的次方-(5-k)x+1-k=0是一元二次方程,求这个一元二次方程的根.
- 7I ( )(我) like it very much
- 8用代入消元法解方程组
- 9改错 1.Not every child like dumplings 2.There is going to have a picnic tomorrow.
- 10sina+cosa=1/5,求sina.cosa
热门考点