If the area and height are known: base = (2 × area) ÷ height
If the perimeter and the other two sides are known: base = perimeter − side 1 − side 2
If the triangle is isosceles and the equal sides and height are known: base = 2 × √(equal side² − height²)
If the triangle is right and the legs are known, the base is one of the perpendicular sides
If the coordinates of the vertices are known, use the distance formula between the two points forming the base
If the altitude splits the base into two equal parts in an isosceles triangle, base = 2 × one half of the base
If the angles and one side are known, use the Law of Sines or Law of Cosines to solve for the base