1) because {C 2 = A 2+B 2-2 ABCOS θ} (known condition c=2, cosθ= 1/2, ab=4).

Therefore, a 2+b 2 = 8, combined with {(a+b) 2 = a 2+b 2+2ab}

Get a = 4 2 √ 3 and b =-(4 2 √ 3).

2)sinC+sin(B-C)=2sin2A is equivalent to sin(A+B)+sin(B-A)=2sin2A, which is simplified as sinB=2sinA and {sinB/sinA=b/a}, so b/a= 1/2 is substituted into {c 2 =.

Note: {Important formula used}