Найдите область значений функции y= 2/sin^4x+cos^4x

[latex]sin^4x=(sin^2x)^2={1\over4}(1-cos2x)^2\\cos^4x=(cos^2x)^2={1\over4}(1+cos2x)^2\\\\sin^4x+cos^4x={1\over4}(2+2cos^22x)={1\over4}(2+cos4x+1)={1\over4}(cos4x+3)\\\\{2\over sin^4x+cos^4x}={8\over cos4x+3}\\\\cos4x\in[-1;1]\\\\{2\over sin^4x+cos^4x}\in[2;4][/latex]