简单三角恒等变换的题:
来源:学生作业帮 编辑:搜搜做题作业网作业帮 分类:数学作业 时间:2024/08/08 18:16:59
简单三角恒等变换的题:
函数f(x)=cos^4 x – sin^4 x – 2sin x cos x可化为( )
A.f(x)=根号2 sin2x
B.f(x)=根号2 sin(2x+兀/4)
C.f(x)=根号2 sin(2x–兀/4)
D.f(x)=根号2 sin(兀/4–2x)
函数f(x)=cos^4 x – sin^4 x – 2sin x cos x可化为( )
A.f(x)=根号2 sin2x
B.f(x)=根号2 sin(2x+兀/4)
C.f(x)=根号2 sin(2x–兀/4)
D.f(x)=根号2 sin(兀/4–2x)
![简单三角恒等变换的题:](/uploads/image/z/15898560-24-0.jpg?t=%E7%AE%80%E5%8D%95%E4%B8%89%E8%A7%92%E6%81%92%E7%AD%89%E5%8F%98%E6%8D%A2%E7%9A%84%E9%A2%98%EF%BC%9A)
f(x)=cos^4 x – sin^4 x – 2sin x cos x
=(cos^2 x – sin^2 x)(cos^2 x +sin^2 x)– 2sin x cos x
=cos^2 x – sin^2 x– 2sin x cos x
=cos2x-sin2x
=√2[sin(兀/4)cos2x-cos(兀/4)sin2x]
=√2sin(兀/4–2x)
=(cos^2 x – sin^2 x)(cos^2 x +sin^2 x)– 2sin x cos x
=cos^2 x – sin^2 x– 2sin x cos x
=cos2x-sin2x
=√2[sin(兀/4)cos2x-cos(兀/4)sin2x]
=√2sin(兀/4–2x)