2(cosA)^2- 1=3/5
(cosA)^2=4/5
CosA=2/ root 5, sinA= 1/ root 5.
SinB= root number 10 10 =1/root10, cosB=3/ root10.
cos(A+B)=cosAcosB-sinAsinB
=2/ root 5X3/ root 10- 1/ root 5X 1/ root 10
= root 2/2
A+B=45 degrees