Maths Problem

Hi all,

If i have a problem of changing:

d^2 (k^1/2)/ dx^2 + d^2(k^1/2)/dx^2 = 0 to

d^2 (phi)/ dx^2 + d^2(phi)/dx^2 = 0

and given that T = k^1/2*phi

How do i change it?