pi=π(读一下就知道...)
cos^4x-2sinxcosx-sin^4x
=(cos^2x+sin^2x)(cos^2x-sin^2x)+sin2x
=cos2x+sin2x
=-√2sin(2x-π/4)
最小正周期:2π/2=π
2x-π/4=-π/2+2kπ(k∈Z)
x=-π/8+kπ
2x-π/4=π/2+2kπ
x=3π/8+kπ
单调递减为【-π/8,3π/8】
最小值为-√2
2x-π/4=π/2+2kπ(k∈Z)
x=3π/8+kπ
pi=π(读一下就知道...)
cos^4x-2sinxcosx-sin^4x
=(cos^2x+sin^2x)(cos^2x-sin^2x)+sin2x
=cos2x+sin2x
=-√2sin(2x-π/4)
最小正周期:2π/2=π
2x-π/4=-π/2+2kπ(k∈Z)
x=-π/8+kπ
2x-π/4=π/2+2kπ
x=3π/8+kπ
单调递减为【-π/8,3π/8】
最小值为-√2
2x-π/4=π/2+2kπ(k∈Z)
x=3π/8+kπ