An obtuse triangle is the laid-back one: a single angle wider than 90 degrees, with the other two squeezed into whatever remains. The long side opposite that wide angle dominates the shape — stretch it and the triangle flattens toward a straight line. Carpenters meet obtuse triangles in hip roofs and stair stringers; landscapers meet them in every irregular yard that refuses to be rectangular. The area formula never changes: half the base times the height, though the height may fall outside the triangle, dropped from the obtuse vertex to an extended base.

The Law of Cosines is the obtuse triangle's best friend, since the Pythagorean theorem only serves right angles. Given two sides and their included obtuse angle, c² = a² + b² − 2ab·cos(C) hands you the third side — and because cosine of an obtuse angle is negative, the correction term adds rather than subtracts, which is why the long side gets so long. This calculator evaluates the area and side arithmetic: enter the base-height or side-angle contributions and read the computed area or side length — enough to price sod for a triangular lawn or check a rafter cut.

With the pre-filled defaults — Variable A 10, Variable B 5 — the Obtuse Triangle Calculator returns Result 50.0000. Change any input and those results update instantly, so you can see exactly how each number you enter moves the answer.