(diagonal length is not a property of a triangle)

edge lengths | a | b | c area | 1/4 sqrt((a + b - c) (a - b + c) (-a + b + c) (a + b + c)) = 0.25 sqrt((a + b - c) (a - b + c) (-a + b + c) (a + b + c)) perimeter | a + b + c interior angles | (cos^(-1)((-a^2 + b^2 + c^2)/(2 b c)) rad | cos^(-1)((a^2 - b^2 + c^2)/(2 a c)) rad | cos^(-1)((a^2 + b^2 - c^2)/(2 a b)) rad)≈(cos^(-1)((0.5 (-a^2 + b^2 + c^2))/(b c)) rad | cos^(-1)((0.5 (a^2 - b^2 + c^2))/(a c)) rad | cos^(-1)((0.5 (a^2 + b^2 - c^2))/(a b)) rad) interior angle sum | 180° = π rad≈3.142 rad (assuming edge lengths a, b, c)