求cos2x+sin2x的单调增区间答得好再附赠

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求cos2x+sin2x的单调增区间答得好再附赠

求cos2x+sin2x的单调增区间答得好再附赠
求cos2x+sin2x的单调增区间
答得好再附赠

求cos2x+sin2x的单调增区间答得好再附赠
令f(x)=cos2x+sin2x
f¹(x)=-2sin2x+2cos2x
=2(cos2x-sin2x)
=2√2cos(2x+π/4)≥0
∴2kπ-π/2≤2x+π/4≤2kπ+π/2
kπ-3π/8≤x≤kπ+π/8 k∈Z
所以cos2x+sin2x的单调增区间为 [kπ-3π/8,kπ+π/8] k∈Z

原式=根号2sin(2x+π/4)
在一个周期内
sinx的递增区间为(-π/2, π/2)
所以sin(2x+π/4)递增区间为(-3π/8,π/8)
所以cos2x+sin2x递增区间为(-3π/8+2kπ,π/8+2kπ)

sin2x+cos2x
=√2(√2/2*sin2x+√2/2cos2x)
=√2(sin2xcosπ/4+cos2xsinπ/4)
=√2sin(2x+π/4)
2kπ-π/2≤ 2x+π/4 ≤2kπ+π/2
kπ-3π/8≤x≤kπ+3π/8
单调增区间
[kπ-3π/8,kπ+3π/8]