NCERT Miscellaneous Example 14 - Sequences and Series
Question: If a, b, c, d and p are distinct real numbers and (a² + b² + c²)p² − 2(ab + bc + cd)p + (b² + c² + d²) ≤ 0, prove that a, b, c and d are in GP.
Answer: b/a = c/b = d/c = p; hence a, b, c and d are in GP.
Full step-by-step NCERT solution with diagrams on Something by Zero.