Nếu \(\int\limits_0^1 {\left[ {{f^2}\left( x \right) - f\left( x \right)} \right]dx = 5} \) và \(\int\limits_0^1 {{{\left[ {f\left( x \right) + 1} \right]}^2}dx = 36} \) thì \(\int\limits_0^1 {f\left( x \right)dx} \) bằng: