Points A (1, 2), B (-3, -1) and C (-4, 5) are the vertices of the triangle. Predefine, acute-angled, obtuse or right-angled is this triangle.

Find the length of the sides: | AB | = √ ((- 3-1) ^ 2 + (- 1-2) ^ 2) = √ (16 + 9) = 5 | ВС | = √ ((- 4 + 3) ^ 2+ (5 + 1) ^ 2) = √ (1 + 36) = √37 | CA | = √ ((1 + 4) ^ 2 + (2-5) ^ 2) = √ (25 + 9) = √34 Equate the square of the larger side to the sum of the squares of the rest: 37 × 34 + 25; 37 <59 If a ^ 2 is less than b ^ 2 + c ^ 2, then the triangle is acute-angled.
Answer: Sharp-angled.