If 4x^4+9x^4=64 then the maximum value of x^2+y^2 is solution) From the eq. finding the value of x^2 and putting it in x^2 + y^2.we get 2nd eq.differentiating that and putting it=0 to get the maximum value we get y^2=16/3.(13)^1/2x^2= 12/(13)^1/2hence. x^2 + y^2=52/3.(13)^1/2 =4.(root 13)/3