（1）角A.B.C成等差数列,
∴2∠B=∠A+∠C;
且内角和∠A+∠B+∠C=π;
∴∠B=π/3;
(2)
sin(A+B)=√2/2;
∵B=60°;
∴A+B=135°,A=135°-60°=75°;
sinA=sin75=sin(30°+45°)=(√6+√2)/2;