The third side of any triangle would be bigger than positive difference of two sides.
The third side will also be less than the sum.
So if we have 4 and 10.
The third side, x
x > (10 - 4)
x > 6
x < (10 + 4)
x < 14
Third side 6 < x < 14.
The third side is any number that is between 6 and 14.
Note: 6 and 14 are not included.