用三角函数的定义证明负根2≤sinA+cosA≥正根2
用三角函数的定义证明负根2≤sinA+cosA≥正根2
数学人气：365 ℃时间：2019-10-31 13:05:51
优质解答
(sinA+cosA)^2=(sinA)^2+(cosA)^2+2sinAcosA=2[(sinA)^2+(cosA)^2]-(sinA-cosA)^2≤2[(sinA)^2+(cosA)^2]=2.所以√2≥sinA+cosA≥-√2.
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