已知函数y=sin2x acos2x的图像关于直线y=
已知函数y=sin2x acos2x的图像关于直线y=-兀/6对称,求实数a的值
设: 函数y=sin2x+acos2x的图像关于直线x=-兀/6对称 令: t = x + 兀/6, 坐标变换, 得: x = t - 兀/6 y = sin2x+acos2x = sin2(t - 兀/6) + a * cos2(t - 兀/6) = [(genhao3 + a) * cos2t]/2 + [(a * genhao3 - 1) * sin2t/2 因为: y(-t) = y(t) 有: [(genhao3 + a) * cos2t]/2 + [(a * genhao3 - 1) * sin2t/2 = [(genhao3 + a) * cos2t]/2 - [(a * genhao3 - 1) * sin2t/2 ==> (a * genhao3 - 1) = 0 a = genhao3/3
y=sin2x +acos2x=(a^2+1)^0.5sin(2x+f),f=arcsina/根号(1+a^2)。图像关于直线y=-兀/6对称, 即2*(-兀/6)+f=0,f=兀/6,sinf=sin30=1/2,a/根号(1+a^2)=1/2, a=正、负(根号3)/3
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