已知谈α=3,则2sin²α-3sinαcosα-1的值为多少?
来源:学生作业帮助网 编辑:作业帮 时间:2024/06/22 03:55:35
![已知谈α=3,则2sin²α-3sinαcosα-1的值为多少?](/uploads/image/z/2729807-71-7.jpg?t=%E5%B7%B2%E7%9F%A5%E8%B0%88%CE%B1%3D3%2C%E5%88%992sin%26%23178%3B%CE%B1-3sin%CE%B1cos%CE%B1-1%E7%9A%84%E5%80%BC%E4%B8%BA%E5%A4%9A%E5%B0%91%3F)
已知谈α=3,则2sin²α-3sinαcosα-1的值为多少?
已知谈α=3,则2sin²α-3sinαcosα-1的值为多少?
已知谈α=3,则2sin²α-3sinαcosα-1的值为多少?
题目应该是tana=3吧
2sin²α-3sinαcosα-1=2sin²α-3sinαcosα-(sin^2a+cos^2a)
=sin^2a-3sinacosa-cos^2a
=(sin^2a-3sinacosa-cos^2a)/(sin^2a+cos^2a)
=(tan^2a-3tana-1)/(tan^2a+1)
=(9-9-1)/(9+1)
=-1/10
不懂,请追问,祝愉快O(∩_∩)O~