If $a, b, c, d$ are non-2ero real numbers sach that $\left.\left(a^2+b^2+c^2\right) b^2+c^2+d^2\righ

Question

If $a, b, c, d$ are non-2ero real numbers sach that $\left.\left(a^2+b^2+c^2\right) b^2+c^2+d^2\right) \leq(a b+b c+c d)^2$, then $a, b, c, d$ are in

Professor PC Thomas Classes · Answer

Saturating the Cauchy-Schwarz bounding explicitly requires strict ratios $a/b = b/c = c/d$, formalizing a GP.