You will need
  • geometric formula to find the area of an isosceles triangle ABC:
  • S = 1/2 x b x h, where:
  • - S - the area of the triangle ABC,
  • - b - the length of its base AC,
  • - h - the length of its height.
Instruction
1
Measure the length of the base AC of an isosceles triangle ABC, usually the length of the base of the triangle is given in terms of the problem. Let the length of the base is equal to 6 cm Measure the height of an isosceles triangle. The height is a segment drawn from the vertex of the triangle perpendicular to its base. Let the conditions of the problem height h = 10 cm.
2
Calculate area of isosceles triangle formula. To do this, divide the length of the base AC in half: 6/2=3 cm, so 1/2b=3 cm. Multiply half the base length as the triangle on the length of the height h: 3 x 10=30 cm, you found the area of the isosceles triangle ABC the length of its base and height. If the length of the altitude is unknown, but given the length of a side of a triangle, then we first find the length of altitude of an isosceles triangle by the formula h = 1/2·√(4a2 – b2).
3
Calculate the length of the height of an isosceles triangle by length of sides and base. Let a be the length of any side of an isosceles triangle, in terms of the problem it is equal to 10 cm Substituting values of the lengths of the sides and base of an isosceles triangle in the formula, find the length of its height h=1/2√(4x100 – 36) =10 cm Calculate the height of an isosceles triangle, to continue the calculation, substituting the found values to the specified formula for finding the area of a triangle by its height and base.