What is the maximum value of the expression?
Algebra
Level
4
Find the maximum value (to 3 decimal places) of
\[\frac {ab + bc + cd}{a^2 + b^2 + c^2 + d^2}\]
for reals \(a\), \(b\), \(c\), and \(d\) which are not all zero.
by
Vijay Simha