Given,
f(x)=∣5x−7∣+[x2+2x]
=∣5x−7∣+[(x+1)2−1]
=∣5x−7∣+[(x+1)2]−1
(as [x−1]=[x]-1 where [.] is greatest integer function)
Now critical points of
f(x)=57,5−1,6−1,7−1,8−1,2
∴ Maximum or minimum value of f(x) occur at critical points or boundary points.
So, f(45)=43+4=419 and f(57)=0+4=4
As both ∣5x−7∣ and x2+2x are increasing in nature after x=57
So, f(2)=∣10−7∣+[4+4]=3+8=11
∴f(57)min=4 and f(2)max=11
So sum of minimum and maximum value is 4+11=15