A属于(派,3/2派),sinA=-√1-cos^2A=-3/5cos^2B=1/(1+tan^2B)=9/10B属于(派/2,派),cosB=-3√10/10sinB=√1-cos^2B=√10/10cos(A+B)=cosAcosB-sinAsinB=2√10/5
