Question 258829
Imagine the two lengths like hands on a clock. 
Since they're a triangle they cannot exactly line up to form a triangle. 
If they were almost on top of each other, like the clock at 12:01, the final leg would be of length,
{{{L=7-4=3}}}
Now imagine they are 180 degrees apart like at 6:00. 
At that point, the final leg would have to be 
{{{L=7+4=11}}} 
Since they cannot be either of those two values, the value can be any number in between them.
{{{3<L<11}}}