Question

What is the first step of the following indirect proof?

Given: The side lengths of a triangle are 4, 4, 6 Prove: The triangle is not a triangle.

Answer 1

The condition for that is
Let a b c be triangle sides they must verify the identities

a + b greater than c
C + a greater than b
B+c greater than a
Sum of two sides is greater than the third

In your case
Sides 4 ,4,6

4 + 4 gt 6
4+ 6 gt 4 true
4 + 6 gt 4 true

Its looks like a vaild triangle sides to me

Answer 2

...it is a triangle...if it's asking to prove it's not a certain type of triangle, I can do that, but the only requirement for a triangle to exist is that the 2 shorter sides added together are greater than the longest side.