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问题: a的值

函数f(x)=[(1+cos2x)/2sin(π/2-x)]+sinx+a^2[sin(x+π/4)]的最大值为(√2)+3,试确定常数a的值

解答:

函数f(x)=[(1+cos2x)/2sin(π/2-x)]+sinx+a^2[sin(x+π/4)]的最大值为(√2)+3,试确定常数a的值
解:f(x)=[(1+cos2x)/2sin(π/2-x)]+sinx+a^2[sin(x+π/4)]
=[(2cos^x)/(2cosx)]+sinx+a^2[sin(x+π/4)]
=cosx+sinx+a^2[sin(x+π/4)]
=√2[√2/2cosx+√2/2sinx]+a^2[sin(x+π/4)]
=√2[sin(x+π/4)]+a^2[sin(x+π/4)]
=(√2+a^2)*sin(x+π/4)
最大值为√2+a^2=(√2)+3
∴a^2=3
a=±√3