Thread:Balu.ur/@comment-26239735-20141028085654/@comment-25501845-20141029113702

From here

https://www.khanacademy.org/math/geometry/congruent-triangles/cong_triangle/v/two-column-proof-showing-segments-are-perpendicular?qa_expand_key=ag5zfmtoYW4tYWNhZGVteXJkCxIIVXNlckRhdGEiRnVzZXJfaWRfa2V5X2h0dHA6Ly9pZC5raGFuYWNhZGVteS5vcmcvNzgzNWZhNjM2ZTk4NGRkOTljYmQ0MjY2YmRiYmI1Y2YMCxIIRmVlZGJhY2sY4doBDA

By the way is this your second profile ?

https://www.khanacademy.org/profile/pranavv3/