2<=3x-4<=5

x=sqrt(a^2cos^2alpha+b^2sin^2alpha)+sqrt(a^2sin^2alpha+b^2cos^2alpha) then x^2=a^2+b^2+2sqrt(p(a^2+b^2)-p^2) , where p is equal to (a) a^2cos^2alpha+ b^2sin^2alpha (b) a^2sin^2alpha+b^2cos^2alpha (c) (1/2)(a^2+b^2+(a^2-b^2)cos2alpha) (d) (1/2)(a^2+b^2-(a^2-b^2)cos2alpha)