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