Answer:
d) 3, 6, 9 cannot be a triangle
Explanation:
According to the first triangle inequality theorem, the lengths of any two sides of a triangle must add up to more than the length of the third side.
So:
a) 3+4 > 5, so yes, this can be a triangle.
b) 5+ 12 > 13, so yes, this can be a triangle.
c) 4 + 6 > 8, so yes, this can be a triangle.
d) 3+6 = 9, it's not MORE than 9, so NO, this cannot be a triangle.