Verified answer

u = x^2 - 1

du = 2xdx

(1/2) ∫ 1/√u du

(1/2) * 2 u^(1/2) + c

= √(x^2 - 1) + c

Cant simplify it to 1/√(x^2 - 1) because thats not what it equals

Integral of x dx/(x^2-1)^(0.5)

u = x^2 - 1, du = 2x dx, so the integrand becomes

(1/2) du / sqrt(u)

whose integral is sqrt(u) + C

= (x^2-1)^(0.5) + C

If you already used "u" in doing the earlier parts of the problem,

then of course use "w" or "z" or something!