Let
f(x)=x3−ax2+bx−c
f′(x)=3x2−2ax+b
f"(x)=6x−2a
f′′′(x)=6
Also,
f′(1)=a
⇒3−2a+b=a
⇒3a=b+3
Also,
f"(2)=12−2a=b
⇒12−2a=3a−3
⇒5a=15⇒a=3
⇒b=6
And,
f′′′(3)=c⇒c=6
Hence,
f(x)=x3−3x2+6x−6
Now,
f(3)+2f(0)=27−27+18−6−12=0
f(2)+f(1)=8−12+12−6+1−3+6−6=0
So,
f(3)+2f(0)=f(2)+f(1)
⇒2f(0)−f(1)+f(3)=f(2)