PDFandMore24Triangle angles must total 180°
The three interior angles of a conventional triangle always add to 180°. For example, 20°, 30° and 25° total only 75°, so they cannot form a triangle. The calculator rejects such input before generating a result.
Required total = 180°
Three side lengths must satisfy the triangle inequality
A set of positive numbers forms a triangle only when the sum of every two sides is greater than the third side.
a + c > b
b + c > a
Area can be calculated with an angle
When two sides and their included angle are known, the area can be found directly with the sine rule for area. This is the SAS case.
Three angles alone do not determine the area
Three valid angles determine a triangle’s shape but not its scale. A 60°–60°–60° triangle can be tiny or very large. One side length is needed to determine actual size, perimeter and area.
Fixed A–B–C convention
This calculator keeps the same naming convention everywhere: A is the lower-left vertex, B is the lower-right vertex, C is the upper vertex, c is the base AB, a is BC and b is CA.