Triangle Inequality
[TEX] \displaystyle \sqrt {(x + 1) ^ 2 + 2 ^ 2} + sqrt {(3-x) ^ 2 + 4 ^ 2} geq sqrt {(x + 1 + 3-x) ^ 2 + ( 2 + 4) ^ 2} = 4 sqrt {13}. [/ TEX]
Equality hold when [TEX]\displaystyle frac {x + 1} {2} = frac {3-x} {4} Rightarrow x = frac {1} {3}. [/ TEX] [/ TEX] [/ TEX][/TEX][/TEX]