f(x) = 2x2 – 5x + 4
∴ f(3x) = 2(3x)2 – 5(3x) + 4
= 2 × 9x2 – 15x + 4
∴ f(3x) = 18x2 – 15x + 4
3f(x) = 3(2x)2 – 5(3x) + 4 × 3
∴ = 6x2 – 15x + 12
∴ 3f(x) = 6x2 – 15x + 12
f(3x) – 3f(x) + 5 = 0 में (3x) और 3f(x) के मान रखने पर
∴ 18x2 – 15x + 4 – (6x2 – 15x + 12) + 5 = 0
∴ 18x2 – 15x + 4 – 6x2 + 15x – 12 + 5 = 0
∴ 12x2 – 3 = 0
∴ 3(4x2 – 1) = 0
∴ 4x2 – 1
∴ x2 = \(\frac{1}4\)
∴ x = ± \(\frac{1}2\)