f(x) = ⁵√x-8 + ⁵√x
f(3x+4)+f(4-3x)=(⁵√3x+4-8 + ⁵√3x+4)+(⁵√4-3x-8 + ⁵√4-3x)=
=⁵√3x-4+ ⁵√3x+4+⁵√-4-3x + ⁵√4-3x=
=⁵√3x-4+ ⁵√3x+4-⁵√4+3x - ⁵√3x-4= 0
f(x) = ⁵√x-8 + ⁵√x
f(3x+4)+f(4-3x)=(⁵√3x+4-8 + ⁵√3x+4)+(⁵√4-3x-8 + ⁵√4-3x)=
=⁵√3x-4+ ⁵√3x+4+⁵√-4-3x + ⁵√4-3x=
=⁵√3x-4+ ⁵√3x+4-⁵√4+3x - ⁵√3x-4= 0