for best books

Below are the best books for your preparation

1- Higher Engineering Mathematics-  B.S Grewal

2- Advanced Engineering Mathematics- Erwin Kreyszig

3- GATE Engineering Mathematics for all Streams- Arihant Publications

4- GATE Engineering Mathematics- Made Easy Publications

All the Best!!

Here are some of the books name for Mathematics you can prefer for GATE & other Exams for same level as well.

Complex Analysis : Schaum Series or J N Sharma.

Numerical Analysis: S.S Sastry.

Differential Equations :  Schaum Series (Frank Ayres

Linear Algebra : A.R. Vasistha (Krishna Series)

Complex Variable : J.N. Sharma (Krishna Series)

Calculus : A.R. Vasistha, Dr. S.K Sharma (Krishna Series)

Calculus : Shanti Narayan (S. Chand)

Vector Calculus : A.R. Vasistha (Krishna Series)

Differential equations: M. D. Raisinghania (S chand)

Complex variables: J.N. Sharma (Krishna Series)

Probability and Statistics : S.C. Gupta and V.K.Kapoor(S chand)

Numerical Method : S.S. Sastry (4th edition)

Graph Theory : Purna chandra Biswal(PHI publication)

Combinatorics : Purna chandra Biswal(PHI publication)

Mathematical Logic: Purna chandra Biswal(PHI publication)

Set Theory & Algebra: Rajendra Akerkar,Rupali Akerkar

Good Luck!