已知x+y=3-cos(4a),x-y=4sin(2a),求x^1/2+y^1/2=2

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已知了x+y和x-y
则x=(3-cos4a+4sin2a)/2
=(3-2cos²2a+1+4sin2a)
=(4-2+2sin²2a+4sin2a)/2
=sin²2a+2sin2a+1
=(sin2a+1)²
y=(3-cos4a-4sin2a)/2
=(3-2cos²2a+1-4sin2a)
=(4-2+2sin²2a-4sin2a)/2
=sin²2a-2sin2a+1
=(sin2a-1)²
x^1/2+y^1/2
=|sin2a+1|+|sin2a-1|
因为-1

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