a

_{1}

^{2}+ a

_{2}

^{2}+ ... + a

_{n}

^{2}

__>__a

_{1}*a

_{2}+ a

_{2}*a

_{1}+ a

_{2}*a

_{3}+ ... + a

_{n}*a

_{n-1}

Such as:

a

^{2}+ b

^{2}+ c

^{2}

__>__ab + ac + bc + ba + bc + ac = 2(ab + bc + ac)

Which can nicely be envisioned geometrically as sum of squares will always be bigger than corresponding sum of rectangles.