函数y=sinx(sinx+cosx) x属于(0,π/2) 求值域

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函数y=sinx(sinx+cosx) x属于(0,π/2) 求值域

函数y=sinx(sinx+cosx) x属于(0,π/2) 求值域
函数y=sinx(sinx+cosx) x属于(0,π/2) 求值域

函数y=sinx(sinx+cosx) x属于(0,π/2) 求值域
y=sinx(sinx+cosx)
=[1-cos(2x)+sin(2x)]/2
=1/2+√2*[sin(2x)*√2/2-√2/2*cos(2x)]/2
=1/2+√2/2*sin(2x-π/4)
0

值域:(0,2)
y=(sinx)^2+sinxcosx=(sinx)^2+1/2*sin2x(2倍角公式)
当x属于(0,π/2)时(sinx)^2属于(0,1),1/2*sin2x属于(0,1)
所以值域:(0,2)

y=sin^2x+sinxcosx=1/2(1-cos2x)+1/2sin2x=1/2+1/2(sin2x-cos2x)=1/2+根号2/2*(sin2xcos(π/4)-cos2xsin(π/4))=1/2+根号2/2sin(2x-π/4)
-π/4<2x-π/4<3π/4,-根号2/20=(1/2-1/2)即0

y=sinx(sinx+cosx)=(sinx)^2+sinxcosx=1/2sin2x+1/2-1/2cos2x=1/2+√(根号)2/2sin(2x-π/4)
所以y属于(0,1/2+√2/2)