Question 583206
Isosceles triangles can indeed be right triangles, as long as the angles are 45, 45, 90.


Otherwise, any other theorem can disprove the statement that JKL is a right triangle, even the law of cosines.


Suppose that a,b,c are the sides, and c is the longest side. Then


*[tex \LARGE c^2 = a^2 + b^2 - 2ab \cos C]


The triangle is a right triangle if and only if cos C = 0, or C = 90. All other triangles cannot be right triangles.