how to reduce a long equation in to a quadratic form equation?

Hi

if

sigx=2.27(Nx/t)+35.5(Del_T)

sigy=.12(Nx/t)-16.0(Del_T)

sigxy=0

if you substitute in the below equation,

(sigx/150000)^2 + (sigx*sigy/(150000^2)) + (sigy/Y)^2 + (sigxy/6000)^2 = 1;

I will get a long equation,,

I want to reduce it to a quadratic equation which would look like,

Nx/t = 110*Del_T + [57.5*(Y^2) - 3000*(Del_T^2)]^0.5

now I know the solution so I'm writing, if the sigx and sigy value changes, I need the solution from matlab.

Please help me, I will be so grateful.

Jagadesh Rao Thalur