y=sin4x+cos4x=√2sin(4x+π/4)
1)最小正周期T=π/2,最小值y=-√2
2)单调增区间:2kπ-π/2什么意思？
先将asinx+bcosx化为Asin(x+ψ)即sin4x+cos4x=√2sin(4x+π/4)
再用T=2π/ω求出周期=T=π/2