find the linearization of y= square root (x+1) using the quadratic approximation?

you want a linear or a quadratic?

in either case, you need to specify a particular point where teh approximation is good near that point. At x=h,

linear: f(x) ≈ f(h) + f'(h)(x-h)
quadratic: f(x) ≈ f(h) + f'(h)(x-h) + 1/2 f"(h) (x-h)^2

so pick a point and plug and chug.