Question

what is formulae for proving a triangle is an isosceles

Answer 1

Prove Triangle Is Isosceles using Coordinate Geometry

Related Links: Regents Prep Coordinate proofs | Triangle Proof | isosceles triangle coordinate proof | images

An isosceles triangle has 2 congruent sides and two congruent angles. The easiest way to prove that a triangle is isosceles using coordinate geometry is to use the sides.

Steps to Coordinate Proof

Given the coordinates of the triangle's vertices, to prove that a triangle is isoscelesplot the 3 points(optional)use the distance formula to calculate the side length of each side of the triangle.If any 2 sides have equal side lengths, then the triangle is isosceles.

Practice Problem 1) The coordinates of triangle BCD are B(8,2), C(11,13) and D(2,6) Using coordinate geometry, prove that triangle BCD is an isosceles triangle.Step 1) Plot Points


Practice Problem 2) Triangle ABC has coordinate A(-2,3) , B (-5,-4) and C (2,-1) Using 
, prove that triangle BCD is an isosceles triangle.Step 1) Plot Points

Answer 2

there is technically no formula for proving a triangle isosceles.

You may prove that a triangle is isosceles by either proving:
◆two opposite sides equal
◆opposite angles are equal