命题q:对任意x∈R,|1+sin2x-cos2x|≤2m|cos(x-π/4)|

问题描述:

命题q:对任意x∈R,|1+sin2x-cos2x|≤2m|cos(x-π/4)|
求m的范围
1个回答 分类:数学 2014-12-10

问题解答:

我来补答
left:
1+sin2x-cos2x=sinx^2+cosx^2+2sinxcosx-(cosx^2-sinx^2)=(sinx+cosx)^2-(cosx+sinx)(cosx-sinx)=(sinx+cosx)(sinx+cosx-cosx+sinx)
right:
2m(cos(x-π/4))=2m(cosxcosπ/4+sinxsinπ/4)=√2m(cosx+sinx)
∵x∈R
∴2|sinx|≤√2m
→m≥√2|sinx|→m∈[√2,+∞)
 
 
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