Question

Find an integer, x, such that 5, 10, and x represent the lengths of the sides of an acute triangle

Answer 1

If a triangle has sides of lengths a and b, with a > b, then the length of the third side, c, is
a - b < c < a + b

Answer 2

Above you see sides of lengths a and b. The sides lie on a line. This is not a triangle, but it shows why the length of the third side needs to be less than a + b.