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问题: 高1数学题6-TOY专问

求值域y=sinx^2+根号3倍的sinxcosx+3cosx^2

解答:

y=(1-cos2x)/2+(3^.5)/2*sin2x+3(1+cos2x)/2
=2+cos2x+(3^.5)/2*sin2x
=2+(7^.5)/2*(sin2xcost+cos2xsint).[t=arctan(2/3^.5)]
=(7^.5)/2*sin(2x+t)+2
--->y属于[2-(7^.5)/2,2+(7^.5)/2]