if you have

y=SQUAREROOT (x^2 + 3)

let z = (x^2 + 3)

...1 dy/dz= 1/2 z ^-1/2 and dz/dx= 2 x <<< can someone explain where the 2 is derived from?

...2 then dy/dz x dz/dx = 1/2 z ^-1/2 (2 x)

...3 this = x/squareroot z = x/SQUAREROOT (x^2 + 3)

how do you get from line 2 to line 3 as x/SQUAREROOT (x^2 + 3)