Hello Student In this post im going to share with you Important Books of Mathematics/Maths Optional Mains for UPSC IAS-Civil Service Examinations you all can buy these imporatnt books from given sources.
Important Books of Maths Optional Mains for IAS-Civil Service Examinations

UPSC/IAS Toppers Recommended Books List for UPSC/CSE-Civil Service Exam of Mathematics Optional Books, IAS UPSC Mains Mathematics/Maths books

Mathematics Optional Paper 1 

Linear Algebra – A.R. Vasistha (Krishna Series)
Schaum's Solved 3,000 Solved Problems Linear Algebra 
Matrices – A. R. Vasistha (Krishna Series)

Advanced Integral Calculus – Dr. D.C. Agarwal ( Krishna Series)
Differential Calculus­– A.R. Vasistha, Dr. S.K Sharma (Krishna Series) 

Ian Sneddon

Solid Geometry – P.N. Chatterjee)
HC Sinha
DK Jha and Sharma

Statics– Krishna Series
Dynamics– Krishna Series

Vector Calculus – Shanti Narayana 
Vector Calculus – A.R. Vasistha & J.N. Sharma 
Curves in Spaces – P.N. Chatterjee (Class Handout)

Mathematics Optional Paper 2

Modern Algebra
Modern Algebra – Vasistha (Krishna Series)Modern Algebra – Herstein (Wiley Publications)

Real Analysis
Elements of Real Analysis – M.D. Raisinghania (S. Chand Series)

Complex Analysis
Complex Analysis –Schaum’s Series
Functions of a Complex Variable –J.N. Sharma Krishna Series

Numerical Analysis
A. R. Vasistha ( Krishna Series)
Numerical Methods – V. RajaRaman
Introductory Methods of Numerical Analysis – Sastry

Linear Programming
Operations Research – Kanti Swarup, P. K. Gupta, ManMohan (S. Chand)Operations Research – S.D.Sharma

Partial Differential Equations (P.D.E)
M.D. Raisinghania ( Refer Paper – M.D. Raisinghania (S. Chand)

Computer Programming
Computer Programming – Class Handout

Mechanics&Fluid Dynamics
Mechanics – S. Chand Publications
Fluid Dynamics – M.D. Raisinghania