Given: g(x)=3f(3x)+f(3−x) and f"(x)>0∀x∈(0,3)
⇒f′(x) is increasing function
⇒g′(x)=3×31⋅f′(3x)−f′(3−x)
⇒g′(x)=f′(3x)−f′(3−x)
It is given that g is decreasing in (0,α) then g′(x)<0.
⇒f′(3x)−f′(3−x)<0
⇒f′(3x)<f′(3−x)
⇒3x<3−x
⇒x<9−3x
⇒x<49
⇒α=49
⇒8α=8×49
⇒8α=18