Для функции Лагранжа L(x, λ) = 3x<sub>1</sub><sup>2</sup> + 5x<sub>2</sub><sup>2</sup>+ λ(x<sub>1</sub> + x<sub>2</sub> − 2) второй дифференциал d<sup>2</sup>L(x, λ) равен: d<sup>2</sup>L(x, λ) = 6dx<sub>1</sub><sup>2</sup> + 10dx<sub>2</sub><sup>2</sup>, d<sup>2</sup>L(x, λ) = 6dx<sub>1</sub><sup>2</sup> − 10dx<sub>2</sub><sup>2</sup>, d<sup>2</sup>L(x, λ) = dx<sub>1</sub><sup>2</sup> + dx<sub>2</sub><sup>2</sup>, d<sup>2</sup>L(x, λ) = dx<sub>1</sub><sup>2</sup> − dx<sub>2</sub><sup>2</sup>