求y=sinx+cosx的单调区间?

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求y=sinx+cosx的单调区间?

求y=sinx+cosx的单调区间?
求y=sinx+cosx的单调区间?

求y=sinx+cosx的单调区间?
y=sinx+cosx
y'=cosx-sinx=√2[√2/2cosx-√2/2sinx]=√2cos(x+π/4)
下面求单调递增区间
y'>=0,
2kπ-π/2 ≤x+π/4 ≤ 2kπ+π/2
2kπ-3π/4 ≤x≤ 2kπ+π/4
单调递增区间[2kπ-3π/4 ,2kπ+π/4]
下面求单调递减区间
y'

y=sinx+cosx
= √2(sinxcosπ/4+cosxsinπ/4)
= √2sin(x+π/4)
x+π/4∈(2kπ-π/2,2kπ+π/2)单调增;x+π/4∈(2kπ+π/2,2kπ+3π/2)单调减
单调增区间(2kπ-3π/4,2kπ+π/4)
单调减区间(2kπ+π/4,2kπ+5π/4)