How do you calculate the area of a triangle without a right angle?
Assume, three sides are given -
Then the Heron's formula gives the area:
Something should be known about a triangle. We need its three independent components, like 3 sides or two sides and angle in between, or two sides and an altitude to the third etc.
The answer above is for three given sides. This is the Heron's formula. If you are interested in a derivation of this formula, you can refer to a course of advanced math for teenagers at UNIZOR and follow the menu options Geometry - Length, Area - Area Problems 1